Question

Can someone explain this to me?


Materials

• Sand and salt
• bowl
• scale
• water

Procedure

CAUTION: Wear goggles and apron at all times.

1. Weigh a clean dry bowl to the nearest 0.01 g. Record this value on Line 1 in the Data Table.

2. Weigh approximately 5.00 g of the salt and sand mixture into the bowl. Reweigh the dish, mixture, and lid. Record this value on Line 2 in the Data Table.

3. Add 10.0 mL of water into the bowl. Carefully stir, taking care not to spill the contents.

4. After allowing the solids to settle, carefully pour out as much water as possib

Answer 1

5. Repeat Steps 3 and 4 three more times.

6. Place the bowl in the oven set on low heat.

7. Carefully heat the bowl until the water has evaporated.

8. Allow the dish and contents to cool, then weigh the dish and lid. Record this value on Line 4 in the Data Table.

Answer 2

Data and Calculations

Mass of evaporating bowl:______________
Mass of evaporating bowl + sample:______________
Mass of sample:__________________
Determining Percent of NaCl in mixture:
Mass of evaporating dish, watch glass, and solids
(after water evaporates):______________
Mass of NaCl:_____________
Percent of NaCl in unknown: _______________



Analysis and Conclusion

1. Show your work on calculating the percentages of each component.


2. Do your percentages add up to 100.0%? If not, why?


3. List at least two sources of error in this lab.


4. Explain what the effect on the percentage of each component would be if the student did not fully dry the evaporating dish after Step 7.

Answer 3

I don't understand how to do the formulas or get the percentages. Also, I don't know what he means on the Analysis and conclusion questions (mostly on question 2 and 4)...

Answer 4

it's comparing the experimental % to the hypothetical 100% in an ideal situation

Answer 5

How do I do that in this situation?

Answer 6

take the mass of the final and compare it against initial and find %

Answer 7

Could you give an example? I don't understand what you mean by 'final' or 'initial'...

Answer 8

for example...if i started with 1g of sugar, mixed it with water, then evaporated the water with heat and ended up with 0.5g of sugar
then 1-0.5 = 0.5
then divide 0.5/1 = 50% recovery, or you ended up with 50% of the original sample

Answer 9

What does it mean when it asks for the "Mass of NaCl"? How would I know how much salt was still in the bowl when there is sand in there too?

Answer 10

Because what's left in the bowl will only be sand, salt would've been dissolved by the water and poured out/evaporated in the oven

Answer 11

Oh I see what you mean. So the 'Percent of NaCl in unknown' is really just 50% since half of it dissolved/evaporated?

Answer 12

No, you take the 10g initially - the sand mass you got left = salt

Answer 13

So their's 0 Mass of NaCI (salt) left since it evaporated, and I get the 10g and minus the sand mass I have left? Why would I want to know how much salt is left ("=salt") if it all evaporate?

Answer 14

*there's

Answer 15

remember, you started with 10g mixture of salt and sand, after salt evaporation, you only have sand remaining. So 10g - sand remaining = mass of salt evaporated

Answer 16

So in the 'NaCI' column, I put how much sand remains, and in the 'percent of NaCI in unknown' column, I put the answer to this equation "10g - sand remaining"?

Answer 17

Corrected: So in the 'Mass of NaCI' column, I put how much sand remains, and in the 'percent of NaCI in unknown' column, I put the answer to this equation "10g - sand remaining"?

Answer 18

mass of NaCl = "10g - sand remaining"
% of NaCl = mass of NaCl /10g

Answer 19

So:

mass of NaCl = 5g (since the salt dissolved out, there's only the initial 5g of sand left)
% of NaCl = 50%

Is that right?

Answer 20

if there is only 5g left of sand, then yes it's correct

Answer 21

wouldn't there only be 5g of sand left since I initially put 5g in, plus the 5g of salt, but then evaporated the salt out, so then there would only be 5g of sand left?

Answer 22

Would it be more 'varied' like 4.3g of salt left if (and when) I really did the expirment?

Answer 23

so you initially knew how much salt you added? i thought you only had a 10g salt/sand mixture of unknown ratios

Answer 24

Well about I said: "2. Weigh approximately 5.00 g of the salt and sand mixture into the bowl. Reweigh the dish, mixture, and lid. Record this value on Line 2 in the Data Table."

Did you mean 5g of salt instead of 10g?

Because when I saw that you said "10g" of the mixture, I thought you were saying they both 5g of salt in and 5g of sand in...?

Answer 25

Corrected: Well above I said: "2. Weigh approximately 5.00 g of the salt and sand mixture into the bowl. Reweigh the dish, mixture, and lid. Record this value on Line 2 in the Data Table."

Did you mean 5g of salt instead of 10g?

Because when I saw that you said "10g" of the mixture, I thought you were saying they both 5g of salt in and 5g of sand in...?

Answer 26

Maybe you thought the 10.0 mL of water that went into the bowl was the grams for the mixture?

Answer 27

What percentages is question 2 asking for? There is only 1 percentage given at the very end of the column... but if there were 2 percentages, why wouldn't they add up to 100%?

Answer 28

ah yes sorry i mean the 5g of the mixture, not 10g