Read solubility curves; what speeds dissolving

Answer Key - Grade 10 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   Esme seals 0.6 L of water under CO₂ at 4 atm and 25 °C. Water holds 1.45 g of CO₂ per liter for each atm. How many grams leave when it opens to 1 atm?

   2.61 g

2. Read this first

   Solubility in 100 g of water (rounded textbook values)

   temperature (°C)	KNO₃ (g)	NaCl (g)	NaHCO₃ (g)
   0	13	36	6.9
   20	32	36	9.6
   40	64	36	12.7
   60	110	37	16.5
   80	169	38	19.7
   100	246	39	23.6

3. 2.

   A saturated KNO₃ solution with 100 g of water at 60 °C cools to 40 °C with no crystals. Jun adds a seed crystal. How much solid forms?

   • 110 g, the whole amount that was dissolved before the solution cooled
   • 46 g: the solution holds 110 g and the 40 °C limit is only 64 g
   • 64 g, the amount that the 40 °C limit lets stay dissolved in the water
4. 3.

   Kira has 150 g of KNO₃ and 100 g of water. All the solid must dissolve, then cool to 20 °C. What is the lowest table temperature to start at, and how much solid forms?

   • 100 °C, giving 246 − 32 = 214 g of crystals
   • 80 °C, giving 150 − 32 = 118 g of crystals
   • 60 °C, giving 110 − 32 = 78 g of crystals
5. 4.

   From 20 °C to 60 °C, how many times as large is KNO₃'s rise in solubility as NaHCO₃'s, Luz?

   • About 11 times (78 g against 6.9 g)
   • About 3 times (32 g against 9.6 g)
   • About 7 times (110 g against 16.5 g)
6. 5.

   A diver breathes air at 3 atm underwater, so extra nitrogen dissolves in the body. What happens on a fast rise to 1 atm, Milo?

   • Nothing changes, since rising does not alter how much gas dissolved
   • The nitrogen dissolves faster, so the body holds even more of it
   • The limit falls, the extra nitrogen leaves solution, and bubbles can form in the tissues
7. 6.

   A bottle holds CO₂ dissolved under 4 atm. It opens to 1 atm at the same temperature. What fraction of the dissolved gas must leave, Noah?

   • Three quarters: at 1 atm only a quarter of the original amount can stay dissolved
   • All of it, because the pressure falls to the outside value
   • One quarter, the part that stays dissolved
8. 7.

   Two bottles from one batch hold the same CO₂, one at 5 °C and one at 30 °C. Both open at 1 atm. Which loses more CO₂, Pia?

   • The cold one: it holds more CO₂ at 1 atm, so more of it can escape
   • They lose the same: both are at 1 atm once they are open
   • The warm one: warm water holds less CO₂ at 1 atm, so more leaves
9. 8.

   Ren says stirring lets a solution hold more sugar, since a stirred cup of 5 g sugar cleared sooner. Sugar's limit is about 200 g per 100 g water. Verdict?

   • Supported: the stirred cup dissolved its sugar sooner, so it can hold more
   • Not supported: 5 g is far below the limit, so only speed changed
   • Supported: stirring raises the limit when a cup clears faster

10. Solubility in 100 g or 100 mL of water (rounded textbook values and HSDB)

    temperature (°C)	KNO₃ (g per 100 g)	NaCl (g per 100 g)	CO₂ (mL per 100 mL)
    0	13	36	171
    20	32	36	88
    60	110	37	36

11. 9.

    Tala claims hot water always dissolves more of any substance. Which data point in the table counters the claim?

    • CO₂: 171 mL at 0 °C falls to 36 mL at 60 °C
    • NaCl: it barely changes, from 36 g to 37 g, so heat does not matter
    • KNO₃: it rises from 13 g at 0 °C to 110 g at 60 °C
12. 10.

    Zee adds 40 g of NaCl to 100 g of water at 25 °C. 36.0 g dissolves and 4.0 g stays. Zee says stirring longer will dissolve the rest. Verdict?

    • Yes: the leftover 4.0 g is too small to be a limit
    • No: 36.0 g is all that dissolves at 25 °C, and stirring cannot add more
    • Yes: given enough stirring, solids dissolve completely