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Solutions and concentrationChemistryHigh schoolabout 0:57

7.455 g of KCl is dissolved in water to make 500 mL of solution. What is the molarity?: animated lesson

A narrated, step-by-step solutions and concentration video lesson with captions. Final answer: M = 0.200005 mol/L.

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Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.4 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
7.455 g of KCl is dissolved in water to make 500 mL of solution. What is the molarity?
2. Step by step
1. $M(\mathrm{KCl}) = 74.548\ \text{g/mol}$
  Molar mass of KCl
2. $n = \frac{m}{M} = \frac{7.455\ \text{g}}{74.548\ \text{g/mol}} = 0.100003\ \text{mol}$
  Convert grams to moles
3. $V = \frac{500\ \text{mL}}{1000} = 0.5\ \text{L}$
  Convert the volume to litres
4. $M = \frac{n}{V} = \frac{0.100003\ \text{mol}}{0.5\ \text{L}} = 0.200005\ \text{mol/L}$
  Molarity is moles per litre
3. The answer
$\text{M = 0.200005 mol/L}$
M = 0.200005 mol/L
4. Check
- n = MV: 0.200005 × 0.5 = 0.100003 mol ✓

Transcript

The problem. Here is the problem: 7.455 g of KCl is dissolved in water to make 500 mL of solution. What is the molarity? Molarity is moles of solute per litre of solution.

Step by step. Molar mass of KCl. Convert grams to moles. Convert the volume to litres. Molarity is moles per litre.

The answer. So the answer is M equals 0.200005 mol/L. Molarity (mol/L, written M) uses the volume of the whole solution, not of the solvent alone. To make a solution, weigh the solute, dissolve it in less solvent, then top up to the final volume.

Check. n equals MV: 0.200005 times 0.5 equals 0.100003 mol, which checks out.

About solutions and concentration

Molarity, dilution and moles of solute in a solution.

7.455 g of KCl is dissolved in water to make 500 mL of…