Grade 7 Science Concentrations of Solutions

Concentration The two cups below each had hot water with a tea bag sitting in them. The time below the cup indicates how long the tea bag has been in the cup.

Concentration is… The quantity of solute that is dissolved in a certain quantity of the solvent. Can be described qualitatively or quantitatively.

_______________ Definition: _______________ _______________ ____________ Definition: ______________ ______________

Dilute vs. Concentrated Dilute There is a small mass of dissolved solute for a certain quantity of solvent. Concentrated There is a large mass of dissolved solute for a certain quantity of solvent

DiluteConcentrated

Describing Concentration… The quantity of solute that is dissolved in a certain quantity of the solution

Qualitative Using words such as like “dilute” or “concentrated” Quantitative Using numbers. This is especially important when safety is an issue!

Student Practice… (page 471) Qualitative or Quantitative? #1(a).Food coloring made the water blue. (b).Adding 3 mL of food coloring turned 250 mL of water blue. Qualitative Quantitative

#2(a).The water became warmer. (b).The water’s temperature increased by 5 degree Celsius. Qualitative Quantitative

#3(a).We needed just over a dozen floor tiles for our model room. (b).We needed 14 floor tiles for our model room. Qualitative Quantitative

#4(a).The liquid boiled in 5 min. (b).The liquid took only a few minutes to boil. Quantitative Qualitative

#5(a).The mass of this solid is 5g more than that one. (b).This solid is heavier than that one. Quantitative Qualitative

#6(a).He drinks eight glasses of water each day. (b).He drinks 2L of water each day. Qualitative Quantitative

Question… If you were a diabetic and had to watch your sugar intake, would you want to know the concentration of a drink qualitatively or quantitatively? Why?

Quantitative Description Expressed as the amount of solute per unit volume. Examples:g/L g/mL ppm (parts per million) %

Converting g/mL to g/L **Remember there are 1000mL in 1 L. 1g/mL = ? g/L 1 x 1000 = 1000 therefore 1000g/L

Practice Problems… 0.3g/mL = ? g/L 300g/L 8.9g/mL = ? g/L 8900g/L

Working with Concentration Units Convert each of the following from mL to L mL = __________________ L 500 mL = ___________________ L 100 mL = ___________________ L 10 mL = ____________________ L 5 mL = _____________________ L 1 mL = _____________________ L

Convert each of the following from g/mL to g/L. 10 g/ 100 mL = __________________ 52 g/ 100 mL = __________________ 65 g/ 100 mL = __________________ 100g/ 100 mL = __________________ 137g/ 100 mL = __________________ 0.15g/ 100 mL = __________________

Saturated vs. Unsaturated Saturated Will form when no more solute will dissolve at a certain temperature Unsaturated More solute is able to dissolve at a certain temperature

Questions to ponder… If there are two glasses of Kool Aid on the table, one is unsaturated and the other is saturated. How would you be able to tell the difference between the two?

2. It is possible to “unsaturate a saturated solution”. Suggest ways you might be able to do this.