Edexcel IGCSE Chemistry 复习笔记 1.5.9 Calculate Concentrations of Solutions-翰林国际教育

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Edexcel IGCSE Chemistry 复习笔记 1.5.9 Calculate Concentrations of Solutions

Edexcel IGCSE Chemistry 复习笔记 1.5.9 Calculate Concentrations of Solutions

Expressing Concentration

A solid substance that dissolves in a liquid is called a?solute, the liquid is called a?solvent?and the two when mixed together form a?solution
Most chemical reactions occur between solutes which are dissolved in solvents, such as water or an organic solvent
Concentration?simply refers to the amount of solute there is in a specific volume of the solvent
The greater the?amount of solute in a given volume then the?greater?the concentration
A general formula triangle for concentration is thus:

1.2.7-Concentration-moles-formula-triangle

The concentration-moles formula triangle?

It is useful to a chemist to express concentration in terms of moles per unit volume
Concentration can therefore be expressed in moles per decimetre cubed
- The units in the answer can be written as mol dm^-3?or mol/dm³:

1.2.7-Concentration-formula-using-moles

You may have to convert from g?dm^-3?into mol?dm^-3?and vice versa depending on the question
- To go from g dm^-3?to mol dm^-3:
  - Divide by the molar mass in grams
- To go from mol dm^-3?to g dm^-3:
  - Multiply by the molar mass in grams

Worked Example

Example 1Calculate the amount of solute, in moles, present in 2.5 dm³?of a solution whose concentration is 0.2 mol dm^-3.

Answer

3.4.1-Calculating-Concentrations-WE1

Worked Example

Example 2Calculate the concentration of a solution of sodium hydroxide, NaOH, in mol dm^-3, when 80 g is dissolved in 500 cm^3?of water.(Na= 23, H= 1, O= 16)

Answer

3.4.1-Calculating-Concentrations-WE2