CHEMISTRY COMMUNITY

Posted: **Sun Oct 06, 2019 12:04 pm**

I've seen in lecture we don't really solve limiting reactant problems by using dimensional analysis like we do in discussion. (In lecture we tend to go through the problems step by step). I understand that its essentially the same process and procedure. On tests, will we get full credit if we just show minimal work (dimensional analysis) like we do in discussion?

Posted: **Sun Oct 06, 2019 12:08 pm**

Yes

In class I usually go through worked examples step by step using and discussing concepts that assist in understanding and therefore developing a strong foundation.

Posted: **Sun Oct 06, 2019 4:41 pm**

Yes, I believe we receive credit based on the correct answer, however the step by step problems in lecture are to understand the process of determining the limiting reagent.

Posted: **Sun Oct 06, 2019 4:44 pm**

I don't think you have to show as many steps as in discussion. However, if you mess up the final answer, but show your correct process, you might receive partial credit.

Posted: **Sun Oct 06, 2019 6:19 pm**

I don't want to be that person but what does dimensional analysis mean?

Posted: **Sun Oct 06, 2019 6:50 pm**

I think I remember hearing that if we have the correct answer for tests, even if you did a short cut or mental calculations and skipped a few steps you will still receive credit. However, I think if you do not have the correct final answer but have shown the steps and working that display the proper procedure, we will still get partial credit for the right steps... so it depends on how you want to do it, but it might also make sense to show the steps for formulating your answer in the event of a calculation error.

Posted: **Sun Oct 06, 2019 7:35 pm**

I think getting to the correct answer is the most important thing, but work helps the grader understand your line of thought. By showing work, you can also learn from your mistakes, i.e. which step you got confused on.

Posted: **Sun Oct 06, 2019 7:40 pm**

We were told in discussion that all that really mattered on the tests was to get the right answer and we would be given credit; however, If we make a math error early on in the problem and carry that error through but complete the rest of the problem correctly we will be given partial credit. In that case with no work you may not receive the partial credit.

Posted: **Sun Oct 06, 2019 9:02 pm**

Do we need to show our work on tests to show how we calculated the correct number of sig figs? Or is our final answer the only thing we are graded on?

Posted: **Sun Oct 06, 2019 10:28 pm**

Natalie Benitez 1C wrote:I don't want to be that person but what does dimensional analysis mean?

Dimensional analysis is the process for solving problems where you multiply out the needed ratios (mole/mole, grams/mole, grams/L) and cancel out the units in order to get the correct answer. You know which ratios you need depending on the balanced equation and knowns you are given.

Posted: **Sun Oct 06, 2019 10:43 pm**

My TA also said that an incorrect answer could still receive some partial credit with the correct work/steps, so I think it is a good idea to show work.

Posted: **Sun Oct 06, 2019 10:56 pm**

I would recommend showing all of your work regardless of the method you use. For free response tests its always better to show more work for partial credit purposes. I feel like showing that you know the process will be more important and get you more credit than getting the answer correct.

Posted: **Sun Oct 06, 2019 11:42 pm**

In my discussion we dont really use dimensional analysis per say so I would think as long as you display some work it would be fine.

Posted: **Sun Oct 06, 2019 11:52 pm**

So we can get partial credit if we show our work and we have the right idea, but mess up the calculations?

Posted: **Sun Oct 06, 2019 11:53 pm**

Is it recommended to just show all of our work when possible? Also, do we need to include the specifications for the element/compound in our calculations?

Posted: **Mon Oct 07, 2019 12:35 am**

Are we going to be expected to know how to write the formula for something like "magnesium sulfate heptahydrate," for example, for the test in our discussions? Or will we just be given chemical symbols?

Posted: **Mon Oct 07, 2019 8:45 am**

briannam_3k wrote:Are we going to be expected to know how to write the formula for something like "magnesium sulfate heptahydrate," for example, for the test in our discussions? Or will we just be given chemical symbols?

I would check with your TA to be completely sure, but the information for the test from Dr. Lavelle says that all equations will be provided. I am also wondering if that includes examples like the one you gave.

Posted: **Mon Oct 07, 2019 10:59 am**

briannam_3k wrote:Are we going to be expected to know how to write the formula for something like "magnesium sulfate heptahydrate," for example, for the test in our discussions? Or will we just be given chemical symbols?

Per my discussion with the UA yesterday at the Chem workshop/review session, I was told that we will likely be provided both the compound name and formula. However, you should still know some of the very common compounds in case.

Posted: **Mon Oct 07, 2019 11:40 am**

If the answer is correct, minimal work with dimensional analysis is fine. However, listing out each step makes it easier for you to check your answer and also increases the possibility of partial credit if you make a mistake on a step midway through.

Posted: **Tue Oct 08, 2019 12:44 am**

Showing work, even if your final answer is incorrect, will always give you partial credit which is important since the tests are 50 points (roughly 7 points/problem if its 7 questions).

Posted: **Tue Oct 08, 2019 8:43 am**

Hi Nate

Dimensional analysis is the way we solve problems and use the multiplication techniques such as 21 grams 1mole/107 grams and the units cancel out.

Posted: **Tue Oct 08, 2019 12:34 pm**

From what I recall, if you get the answer correct, then you are given full credit as long as some work is shown. However, I would still show work in case I get the problem wrong and my work shown will be worth some partial credit.

Posted: **Tue Oct 08, 2019 3:20 pm**

I would show some work just in case but I read that as long as you show some work you'll get partial credit

Posted: **Tue Oct 08, 2019 3:31 pm**

Yes, as long as you follow all of the steps to show the limiting reactant calculations you should receive full credit.

Posted: **Tue Oct 08, 2019 10:45 pm**

Do we have to have the formulas of the polyatomic ions memorized?

Posted: **Thu Oct 10, 2019 12:08 am**

Because each question is worth so many points, it would be wise to show at least the basic steps that you used to get to your solution.

Posted: **Thu Oct 10, 2019 3:04 pm**

Yes, however I think it is best to show work so that in case you make a mistake you may receive partial credit.

Posted: **Thu Oct 10, 2019 8:39 pm**

ktran Disc 1I wrote:Is it recommended to just show all of our work when possible? Also, do we need to include the specifications for the element/compound in our calculations?

I think the safe bet is to always show every step with the specifications for an element or compound just in case.

Posted: **Thu Oct 10, 2019 8:43 pm**

KatherineValdez_4B wrote:So we can get partial credit if we show our work and we have the right idea, but mess up the calculations?

yes I remember my TA saying we get partial credit for calculations and showing work.

Posted: **Thu Oct 10, 2019 9:19 pm**

For limiting reactants on the test do we have to explain how we know one is a limiting reactant or can we just specify which one?

Posted: **Fri Oct 11, 2019 9:17 am**

I think it would be best to show your work how you learned it rather than confusing yourself by adding minor steps. However, the minor steps might help you receive partial credit if your answer is incorrect. :)

Posted: **Fri Oct 11, 2019 9:55 am**

Cassandra_1K wrote:For limiting reactants on the test do we have to explain how we know one is a limiting reactant or can we just specify which one?

You should show the work for how you found the limiting reactant. Even if you're wrong, you would be able to get partial credit for explaining.

Posted: **Fri Oct 11, 2019 11:29 am**

You definitely receive credit for coming to the correct answer but in order to get the most partial credit possible you should write it out step by step.

Posted: **Fri Oct 11, 2019 12:05 pm**

when it comes to answering anything on a test I recommend underlining what it's asking you for and make sure you answer completely. Show full work of what it's asking you, and just that, no need for unnecessary work.

Posted: **Fri Oct 11, 2019 1:10 pm**

Show as much work as you can when solving the problems on the test in order to receive as much partial credit as you can!

Posted: **Fri Oct 11, 2019 4:21 pm**

so we do receive partial credit?

Posted: **Sat Oct 12, 2019 10:54 am**

When in doubt, survival by partial credit! Probably best to show your work so your TA is following along with you during the problem.

Posted: **Sat Oct 12, 2019 12:55 pm**

Showing your work can also make it easier for you to double check your answers too!

Posted: **Sat Oct 12, 2019 1:33 pm**

Showing your work in terms of dimensional analysis also makes it clearer in terms of what factor you need to divide or multiply by.

Posted: **Sat Oct 12, 2019 8:32 pm**

Showing work is best because the TA can follow along every step and give you max points for each step.

Posted: **Sat Oct 12, 2019 9:27 pm**

I think it's best to be safe and show all work. However, it really depends on what TA you have.

Posted: **Sun Oct 13, 2019 8:50 am**

I think that you definitely need to show the mole to mole rations for limiting reactant problems on the tests, as those are the key parts of the problem that Dr. Lavelle wants you to understand.

Posted: **Sun Oct 13, 2019 11:56 am**

I don't think that every single simple step needs to be shown, but someone who does not know much about chemistry or who would be confused easily should be able to follow along and understand how you got from point A to B.

Posted: **Sun Oct 13, 2019 11:57 am**

Cassandra_1K wrote:For limiting reactants on the test do we have to explain how we know one is a limiting reactant or can we just specify which one?

just specify which one

Posted: **Sun Oct 13, 2019 12:26 pm**

My TA informed us on Monday that if we have the correct answer we get full credit, but if we don't have the correct answer we can get partial credit if the work we've shown is correct but a calculation was messed up

Posted: **Sun Oct 13, 2019 12:32 pm**

Yes, I believe you will get credit as long as you show your work.

Posted: **Sun Oct 13, 2019 12:54 pm**

When showing work it's important to include the right units in your work.

Posted: **Sun Oct 13, 2019 4:15 pm**

I made sure to use dimensional analysis to make it clear when units canceled out.

Posted: **Sun Oct 13, 2019 4:20 pm**

You don’t have to show as much work. However, it may help so if you make a calculating mistake, graders can see each step and you can get partial credit for completing the steps correctly even with a calculating error.

Posted: **Sun Oct 13, 2019 6:54 pm**

When showing work, I always include units from beginning to end, which makes it easier for the grader to follow as well as serves as a way to check if I got the right answer based on getting down to the right units.

Posted: **Sun Oct 13, 2019 6:59 pm**

I have a question about significant figures. What number do we base the amount of significant figures we use? Like in any problem.

Posted: **Sun Oct 13, 2019 7:25 pm**

KatherineValdez_4B wrote:I have a question about significant figures. What number do we base the amount of significant figures we use? Like in any problem.

Usually we round the sig figs based on those given in the question, seen when numbers are given with excess zeros after decimal(0.500). Try to not round early in the question if possible until the end to preserve accuracy.

Posted: **Sun Oct 13, 2019 8:55 pm**

KatherineValdez_4B wrote:I have a question about significant figures. What number do we base the amount of significant figures we use? Like in any problem.

You base the number of significant figures of your answer on the least number of significant figures given in the question. For example, given the question, "A solution is prepared by dissolving 55.1g (three sig figs) of KCl in approximately 75mL (two sig figs) of water and then adding water to a final volume of 125mL (three sig figs). What is the molarity of KCl in this solution?"
The answer would be written as 5.9M (two sig figs) because the least number of sig figs in the question is two (look at 75mL)

Posted: **Sun Oct 13, 2019 9:45 pm**

claudia_1e wrote:
Natalie Benitez 1C wrote:I don't want to be that person but what does dimensional analysis mean?

Dimensional analysis is the process for solving problems where you multiply out the needed ratios (mole/mole, grams/mole, grams/L) and cancel out the units in order to get the correct answer. You know which ratios you need depending on the balanced equation and knowns you are given.

This method is also called the Factor Label Method if that is how you are familiar with it

Posted: **Sun Oct 13, 2019 10:12 pm**

yes as long as you have the correct answer and the grader can tell what you did then you'll get credit

Posted: **Sun Oct 13, 2019 10:58 pm**

I believe partial credit is awarded for steps within the overall problem.

Posted: **Tue Oct 15, 2019 10:19 pm**

KatherineValdez_4B wrote:I have a question about significant figures. What number do we base the amount of significant figures we use? Like in any problem.

The amount of significant figures we use is based on the amount of significant figures in the values given in the question.

Posted: **Sat Oct 19, 2019 7:30 pm**

I would show all work. I had points taken off my first test for not showing work in some parts. You don't have to show everything step by step, but as long as it shows your calculations you should be fine. If you feel you should have gotten more points for the work you showed you can always talk with the TA's , they're very helpful

Posted: **Sun Oct 20, 2019 2:26 pm**

When doing any problem, do we have to show the steps for the units?
Like do we have to show how the units change in order to get the final unit?

Posted: **Sun Oct 20, 2019 2:27 pm**

I'm sorry I realize I might not have made much sense in my last question.

Posted: **Sun Oct 20, 2019 2:29 pm**

AGaeta_4E wrote:
KatherineValdez_4B wrote:I have a question about significant figures. What number do we base the amount of significant figures we use? Like in any problem.

You base the number of significant figures of your answer on the least number of significant figures given in the question. For example, given the question, "A solution is prepared by dissolving 55.1g (three sig figs) of KCl in approximately 75mL (two sig figs) of water and then adding water to a final volume of 125mL (three sig figs). What is the molarity of KCl in this solution?"
The answer would be written as 5.9M (two sig figs) because the least number of sig figs in the question is two (look at 75mL)

Thank you so much, this was very helpful!

Posted: **Sun Oct 20, 2019 2:31 pm**

405335722 wrote:
KatherineValdez_4B wrote:So we can get partial credit if we show our work and we have the right idea, but mess up the calculations?

yes I remember my TA saying we get partial credit for calculations and showing work.

Thank you!! Imma need that partial credit.

Posted: **Mon Oct 21, 2019 12:07 am**

KatherineValdez_4B wrote:
405335722 wrote:
KatherineValdez_4B wrote:So we can get partial credit if we show our work and we have the right idea, but mess up the calculations?

yes I remember my TA saying we get partial credit for calculations and showing work.

Thank you!! Imma need that partial credit.

I messed up on this question because I mixed up my ratio which in turn resulted in me getting the wrong answer so imma talk to my TA too haha thanks

Posted: **Mon Oct 28, 2019 10:54 am**

KatherineValdez_4B wrote:When doing any problem, do we have to show the steps for the units?
Like do we have to show how the units change in order to get the final unit?

I believe you don't have to but showing all the units in your dimensional analysis helps with avoiding mistakes and allows for partial credit to be awarded if you do end up messing up for the final answer.

Posted: **Mon Oct 28, 2019 4:52 pm**

In addition to showing all units, it would be helpful to clearly split the limiting reaction question into 3 parts: (1) the type of amount for which you are calculating, (2) the dimensional analysis to compare amounts for compounds (3) determination of excess after determining limiting reactant.

Posted: **Wed Oct 30, 2019 8:16 pm**

Only your final answer needs correct units

Posted: **Thu Oct 31, 2019 11:22 am**

So do we have to have exact units for each step of the problem, or just correct units for the answer?

Posted: **Fri Nov 22, 2019 2:04 pm**

Your final answer needs to have correct sig figs for full points I believe, and I think there is partial credit for longer problems.

Posted: **Sat Nov 23, 2019 8:57 pm**

Only your final answer needs the correct sig fig amount. However, I remember a post that also mentioned for each individual step you only need to round for the final sig fig number. This way, any rounding errors you may have are okay as long as you use the correct number of sig figs as the final answer when rounding in each step.

CHEMISTRY COMMUNITY

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