GRADE 7 SCIENCE

Solutions

Solutions… a review

A homogeneous mixture

They appear as ONE substance

Examples: tap water, vinegar, gold jewelry

We will learn:

identify the solute and the solvent in a variety of solutions

distinguish between soluble and insoluble substances

describe the concentration and solubility of substances qualitatively and quantitatively

Solutions have 2 parts:

SoluteThe substance that dissolves (found in less amounts)

SolventThe substance in which the solute dissolves (found in the greatest amounts)

Solute= Salt in this case

Solvent= Water

Page 255: Solute or Solvent?

A. Brass is used to make many objects. Brass is a solution of zinc metal in a copper metal.

B. Hydrogen peroxide is used to disinfect cuts. Hydrogen peroxide is a solution of 3% hydrogen and 97% water.

Solute or Solvent? C. Dental amalgam is a metal

that is used to fill cavities. It is a solution of mercury in tin.

D. Deicing fluid is a cleaner used to clean car and truck windshields. It is made up of a solution of propylene glycol in water.

Solutions song!- Journey with Me! http://www.youtube.com/watch?v=3G472AA3SEs

Dissolving...To mix completely (the solute dissolves into the solvent.)

Some substances are able to dissolve better than others.

For those about to dissolve- we solute you!

http://www.youtube.com/watch?v=VTmfQUNLlMY

The Particle Theory of Matter states that “there are attractive forces between the particles”.

How are substances soluble?

In order to dissolve, the particles must be more

strongly attracted to the particles of the solvent than to

themselves. This means that the solute is

soluble in that solvent.

If something is ABLE to dissolve then it is soluble.

For example, sugar dissolves in water.

Particle Theory- Dissolving animation

If the particles of the solute are more attracted to their own particles than the solvent particles, dissolving does NOT occur. The solute is said to be insoluble in that solvent. (ie. Mechanical)

How are substances insoluble?

If something is UNABLE to dissolve then it is insoluble.

For example, sand does not dissolve in water.

Soluble or Insoluble?

soluble

insoluble

Solvent or Not?

Some materials are good solvents for some solutes but not others. For example, oil is insoluble in water but soluble in gasoline.

States of Solutes and Solvents- Put book and workbook away. Hand out exit cards. Below is an example!

AirSolute: oxygen, carbon dioxide, other gases

Solvent: nitrogen (most of our air is actually Nitrogen!!) Gas

Gas

Soda:(a combination of carbon dioxide in water). Identify water or carbon dioxide as the solute/solvent and say which state they are.

Solute: ?

Solvent: ?

State of Solute: ?

State of Solvent: ?

Vinegar:(a combination of 3% acetic acid and 97% water). Identify water or acetic acid as the solute/solvent and say which state they are.

Solute: ?

Solvent: ?

State of Solute: ?

State of Solvent: ?

Filtered Sea Water: (salt in water). Identify water or salt as the solute/solvent and say which state they are.

Solute: ?

Solvent: ?

State of Solute: ?

State of Solvent: ?

Brass

(an alloy of a zinc metal in a copper metal) Identify zinc or copper as the solute/solvent and say which state they are.

Solute:?

Solvent: ?

State of Solute: ?

State of Solvent: ?

Grade 7 Science

Concentrations of Solutions

Concentration (p 4 of workbook; 264)

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.

 

10 minutes 2 minutes

Concentration is… The quantity of solute that is dissolved in a certain quantity of the solvent.

Can be described qualitatively or quantitatively.

Qualitative:

Using words such as like “dilute” or

“concentrated”

Quantitative:

Using numbers. This is especially important when safety is an issue!

Student Activity…

1. Demo of qualitative concentration

2. Demo of quantitative concentration

Student Practice… 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

Dilute vs. Concentrated

DiluteThere is a small mass of dissolved solute for a certain quantity of solvent.

ConcentratedThere is a large mass of dissolved solute for a certain quantity of solvent

Dilute vs. Concentrated- Explained Qualitatively

Dilute vs. Concentrated- Explained Quantitatively

Saturated vs. Unsaturated

SaturatedWill form when no more solute will dissolve at a certain temperature

Unsaturated

More solute is able to dissolve at a certain temperature

Question to ponder…

Can a solution be considered to be concentrated be unsaturated? Explain

Question to ponder…

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

Question to ponder…2. It is possible to “unsaturate a saturated solution”. Suggest ways you might be able to do this. (Hint: How could you make more sugar dissolve in a glass of water?)

GRADE 7 SCIENCESolutions and Solubility

How Does Temperature Affect Solubility?

Complete Core Activity 8-2A page 268-9

Rate of Dissolving…Factors that affect the rate of dissolving include:

Size of the soluteTemperaturePressure

Size of SoluteThe smaller the solute particles, the quicker they will dissolvefaster

TemperatureThe higher the temperature, the more solute and the faster the solute will dissolvefaster

PressureGases are more soluble in liquids under higher pressure (see page 267)

Opened bottle decreases pressure and “bubbles” come out of solution

Quantitative Description

Expressed as the amount of solute per unit volume.

Examples: g/Lg/mLppm (parts per

million)%

Converting g/mL to g/L**Remember there are 1000mL in 1 L.

1g/mL = ? g/L1 x 1000 = 1000

therefore 1000g/L

Practice Problems…

0.3g/mL = ? g/L300g/L

8.9g/mL = ? g/L8900g/L