Lesson No: 7   Unit Title: Solutions
 Lesson 2Lesson 3Lesson 4Lesson 5

 

Unit No:

7H

Lesson Title

A soluble problem

 

NC Ref:  lh 2b

 

--Objectives:

MK - Solids dissolve better in hot water. Factor, Variable.

SK - There is a limit to the amount of solid that will dissolve in water. This limit is different for different solutes, more dissolves in hotter water. Speed is often more important than amount. Temp affects speed of dissolving. Saturated, Solubility. CK - Quantitative solubility, gases follow opposite rules, S.A and speed of dissolving

           

 

Lesson outline:

MK/SK

•    Introduce idea by making a cup of tea and adding a large amount of sugar. Will it all dissolve — discussion leading to saturation and dissolves quicker if tea is hot. Could demonstrate this with hot and cold water in a beaker then drop a sugar lump in each.

•    Practical — Students to investigate how temperature affects solubility using MK — 7He/1

•    Lead towards a particle model of dissolving and why temperature allows us to dissolve more. Molymods and sugar cubes are a good way of getting this across (see MJH if unsure)

•    Demonstration — add equal volumes of lead nitrate and potassium iodide. A precipitate is formed. Heat until almost boiling, the precipitate dissolves. Allow to cool and the crystals reform as a golden snowstorm’ effect. This reinforces the idea of solubility and temperature.

•    Plenary — MK — That solids dissolve better in hot water. W/s 7He/4

                     SK — Saturation, solubility and temp and rate of dissolving

with temp.

•    Extension activity — how fast does sugar dissolve? Students to pick a variable eg temp, amount of solute, vol of solvent, surface area (lumps vs granulated).

•    Exploring Science P100—101. 

 

 

Homework: 7He/3 Solutions crossword

 

 

Resources: 7He/1 7He/3 7He/4  Salt, sugar, mass balances, spatulas, potassium chloride (labelled salt for temperature practical), boiling tubes, kettle, lead iodide 0.005M solution, lead nitrate 0.005M solution.  Word sheets and summary.

 

 

Risk Assessment: safety glasses. Lead compounds are toxic. Only allow students to carry out the ‘golden snowstorm’ experiments if trusted otherwise demonstrate.