Are my answers to these Chemistry problems correct?

Question

1. What is the molality of a solution formed when 80.0 moles of Potassium Hydroxide (KOH) are mixed with 5.4 kg of water?

A. 1.5 M

B. 1.5 m

C. 14.8 m

D. 14.8 M

E. None of the Above

 

2. For the reaction 3Na₂SO₄ (aq) + 2Al(NO₃)₃ (aq) → Al₂(SO₄)₃ (s) + 6NaNO₃ (aq), adding 960.0 ml of 5.20 M Aluminum Nitrate to excess Sodium Sulfate will produce how many grams of Aluminum Sulfate?

A. 4.99 mol Al(NO3)3

B. 856 mol Al2(SO4)3

C. 296.4 g Al2(SO4)3

D. 499 g Al(NO3)3

E. None of the Above

 

3. Calculate the freezing point of a solution formed when 55.0 g of NH₃ are mixed with 820.0 g of water. (NOTE: NH₃ does not dissolve into multiple ions; each molecule dissolves as an individual whole. Also, the K_f of water is 1.86 ^oC/m.)

A. –14.3 oC

B. –7.33 oC

C. 0.00 oC

D. 7.33 oC

E. 14.3 oC

 

4. For the reaction NaBr (aq) + AgNO₃ (aq) → AgBr (s) + NaNO₃ (aq), how many liters of 4.5 M Silver Nitrate (AgNO₃) would be required in order to mix with adequate Sodium Bromide (NaBr) to produce 250.0 g of Silver Bromide (AgBr)?

A. 0.25 mL NaNO3

B. 0.25 L NaNO3

C. 0.30 mL AgNO3

D. 0.30 L AgNO3

E. None of the Above

 

5. Water in a hot tub is maintained at 100.4 ^oF, and contains several solid solutes to keep it safe. What will happen if the temperature is permitted to fall significantly?

A. It will get cloudy and fill with a fine solid.

B. It will become unsafe to occupy.

C. The water level will rise significantly.

D. Oxygen will bubble out of the water.

E. Hydrogen will bubble out of the water.

Answer 1

Hi Jesset C.,

1 looks good (assuming the KOH can dissolve that much!)

2 looks good, they tried to sucker you in with B, which was correct as GRAMS, not moles!

3 looks good, I think you might be able to do that mentally, since MW NH3 ~ 17 which is about 55/3

4 is incorrect, try re-working it, you should get D, I figure.

5 is the best choice, although it is by no means certain that the solutes will precipitate out! it depends on their individual identities (as well as any cross-reaction products of their various ions, that's called metathesis, by the way). It would not be usual to load up a hot tub with salts, even though that might make it less likely to sustain bacterial or algal growth -- you would tend to shrivel like a prune when you soaked! It might also be worth noting that natural hot springs are sometimes infested with Naegleria fowleri (brain-eating ameba), which is discouraged by salt.

--Cheers, --Mr. d.