Name________________
1. Suppose you had a beaker that contained 50 grams of salt-water mixture. It contains 12 grams of NaCl. What's the percent concentration of this mixture?
2. What would be the % concentration of a solution containing 15 grams of sucrose dissolved in 85 grams of water?
3. Suppose you were given a bottle that contains 400 grams of a 3.0% bleach solution. What mass of solute is in this bottle?
4. Suppose you have some 3.5% salt solution. You need to obtain a total of 14 grams of salt. How many grams of the 3.5% solution would you use.
5. What units are used to measure the solubility of a gas in water?
6. Give the chemical formula for the dissolved oxygen found in a lake or stream.
7. Which of the following substances is a typical product of anaerobic decomposition?
(a) CO2 (b) NaCl (c) NH3 (d) glucose
Metric conversions:
(8) How many milligrams are there in 1000 grams?
(9) How many meters equal 92.5 centimeters?
10. What is the % concentration of a solution containing 10.0 grams of sucrose in 1,000 gram mixture?
11. If a substance is biodegradable, and it sinks to the bottom of the lake, then what will happen to it?
12. Where, in a big lake, would you expect to find aerobic
conditions, if there are any to be found at all?
13. Which ELEMENT is usually the LIMITING nutrient in lake
waters in Maine?
14. We don't want sewage seeping into our favorite lake because
(pick one):
(a) it can contain substances that act as fertilizer for algae
(b) it may contain disease organisms
(c) it may contain poisonous substances
(d) all of the above.
15. A vitamin supplement tablet that contains 0.06 grams of vitamin C supplies 100% of the RDA. This mass of vitamin C can also be expressed as (pick one):
(a) 6 mg (b) 60 mg (c) 600 mg (d) .006 kg
16. Suppose you have a solution of KNO3; you find that it is a 6.0% KNO3 solution. What would be the mass of KNO3 dissolved in 300 mL of solution?
17. Excessive amounts of algae are harmful to the ecology of
our favorite lake because:
(a) as they grow they give off by-products that are poisonous
(b) their rapid growth uses up oxygen that fish need to survive
(c) When they die, their decay uses up dissolved oxygen
(d) They provide too much food for the aquatic food web, producing obese fish.
18. The photosynthesis process ordinarily uses up WHAT gas?
19. What happens to the solubility of solids such as KNO3 when the temperature of the water rises?
(a) it increases
(b) it decreases
(c) it fluctuates up and down
(d) no statement can be made about changes in solubility.
Refer to the attached data table for Branch Lake to answer the following questions.
20. On March 26 -- why is the warmest water located at the bottom of the lake?
21. On March 26 -- at what depth was the greatest concentration of dissolved oxygen found? (Pick one.)
(a) at the bottom (c) in the middle
(b) at the top (d) at the same depth as on Sept. 23
22. How did the dissolved ammonia level at the bottom of the lake change from March 26 to Sept 23? (Pick one.)
(a) On March 26 it was greater
(b) On Sept 23 it was greater
(c) There was no change
23. How can you explain the extremely high level of dissolved oxygen (14.4 mg/L) found in the lake on March 26?
(a) there was a great deal of aeration occurring under the ice
(b) the water was very cold
(c) photosynthesis occurs rapidly at the temperature found at that spot.
(d) the migrating fish stirred up the water with their energetic swimming efforts
24. The transparency found on the two dates of March 26 and September 23 can be described how? (Pick one.)
(a) It was quite poor on both dates.
(b) It was quite poor in March but quite good in September
(c) It was quite good in March but poor in September
(d) It was quite good on both dates
25. We have learned that a total phosphorous concentration of
15 ppb (.015 mg/L) can trigger an algae bloom. When during the course of the year (March to November) was it likely that an algae bloom occurred in this lake?
Chemistry Test - Percent Solutions
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Questions? Comments??
Bob Clark