Read solubility curves; what speeds dissolving

Answer Key - Grade 10 Science Worksheet

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

1. 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

2. 1.

   Esme cools a saturated KNO₃ solution made with 250 g of water from 100 °C to 40 °C. How many grams of KNO₃ crystallize?

   455 g
3. 2.

   A solution holds 90 g of KNO₃ in 100 g of water at 60 °C and cools slowly. When does solid first appear, Jun?

   • Between 40 °C and 20 °C, where the limit drops from 64 g to 32 g, below 90 g
   • Between 60 °C and 40 °C, where the limit falls from 110 g to 64 g
   • At 60 °C, because 90 g is already close to the 110 g limit there
4. 3.

   KNO₃ has a little NaCl mixed in. Kira wants pure KNO₃ crystals. Which plan works best?

   • Dissolve in cold water and filter: KNO₃ dissolves, but the NaCl stays on the paper as solid
   • Dissolve in hot water, then cool it: only KNO₃ crystallizes and the NaCl stays dissolved
   • Evaporate the water away: the dish keeps the KNO₃ and the NaCl is lost in the vapor
5. 4.

   A hot saturated NaCl solution cools from 80 °C to 20 °C. About how much NaCl crystallizes per 100 g of water, Luz?

   • About 137 g, the same drop as KNO₃
   • About 38 g, nearly the whole amount, as with KNO₃
   • About 2 g: NaCl's limit barely changes, so most stays dissolved

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

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

7. 5.

   CO₂ falls from 171 to 88 mL between 0 and 20 °C, then to 36 mL by 60 °C. What does this show about the curve, Milo?

   • It falls fastest in cold water: about 4 mL per °C at first, then 1.3
   • It falls fastest in hot water, about 4 mL per °C between 20 °C and 60 °C
   • It falls at one steady rate, about 2.3 mL per °C, from 0 °C right up to 60 °C
8. 6.

   At 20 °C and 1 atm, water holds 88 mL of CO₂ per 100 mL. A bottle is filled at 20 °C under 3 atm of CO₂. How much dissolves, Noah?

   • About one third as much, because higher pressure squeezes gas back out of the water
   • About three times as much, since dissolved gas is proportional to its pressure
   • The same amount, because temperature alone changes how much gas dissolves in water
9. 7.

   A power plant sends warm water into a river. Fish need dissolved oxygen. Using the gas trend, what is predicted, Pia?

   • More dissolved oxygen, because warm water mixes gases faster
   • Less dissolved oxygen, because gases dissolve less in warmer water
   • No change, because the river's air pressure stays the same

10. Time for 5.0 g of table salt to dissolve in 100 mL of water (example data)

    trial	temperature (°C)	crystals	stirred	time (s)
    1	20	coarse	no	95
    2	20	coarse	yes	40
    3	20	fine	yes	12
    4	40	fine	yes	7

11. 8.

    Which two trials show the effect of temperature alone, Ren?

    • Trials 2 and 4: temperature and crystal size both change
    • Trials 1 and 4: temperature, stirring and crystal size all change
    • Trials 3 and 4: only the temperature changes
12. 9.

    Tala says the 12 s in trial 3 shows fine crystals hold more salt. NaCl's limit is 36 g per 100 g water. Verdict?

    • Supported: 12 s is the fastest time among the first three trials
    • Not supported: 5.0 g is far below the 36 g limit, so only the speed changed
    • Supported: fine crystals dissolved in less time, so more salt can fit in the water
13. 10.

    Why does crushing a solid speed up dissolving but not change the limit, Zee?

    • Crushing turns the solid into a more soluble substance
    • Crushing warms the solid, which raises the limit
    • More surface meets the water at once, but temperature and the substance set the limit