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Chapter 12: Q30P (page 285)

What is meant by water hardness? Explain the difference between temporary and permanent hardness.

Short Answer

Expert verified

Water hardness is the measure of total concentration of Ca2+, Mg2+ or Fe2+ (basically cations) in water. The main difference between temporary and permanent hardness is the removal technique. Temporary hardness of water can be removed by boiling water whereas permanent hardness cannot be removed by boiling.

Step by step solution

01

Water Hardness

Water hardness is the measure of total concentration of Ca2+, Mg2+ or Fe2+ (basically cations) in water.

02

Permanent and Temporary Hardness

The carbonates and bicarbonates salts of calcium and magnesium causes temporary hardness in water. Permanent hardness in water is caused by the presence of sulfates and chlorides of calcium and magnesium.

03

Difference between Permanent and Temporary Hardness

The main difference is the removal technique. Temporary hardness of water can be removed by boiling water whereas permanent hardness cannot be removed by boiling.

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Most popular questions from this chapter

Calculate pCu2+ (to the 0.01 decimal place) at each of the following points in the titration of 50.0 mL of 0.040 0 M EDTA with 0.080 0 M Cu (NO3)2 at pH 5.00: 0.1, 5.0, 10.0, 15.0, 20.0, 24.0, 25.0, 26.0, and 30.0 mL. Make a graph of pCu2+ versus volume of titrant.

Spreadsheet equation for auxiliary complexing agent. Consider the titration of metal M (initial concentration = CM, initial volume = VM) with EDTA (concentration = CEDTA, volume added = VEDTA) in the presence of an auxiliary complexing ligand (such as ammonia). Follow the derivation in Section 12-4 to show that the master equation for the titration is

ϕ=CETDAVETDACMVM=1+Kf"[M]free-[M]free+Kf"[M]freeCMKf"[M]free+[M]free+Kf"[M]free2CETDA

where role="math"> is the conditional formation constant in the presence of auxiliary complexing agent at the fixed pH of the titration (Equation 12-18) and [M]free is the total concentration of metal not bound to EDTA. [M]free is the same as [M] in Equation 12-15. The result is equivalent to Equation 12-11, with [M] replaced by [M]free and Kf replaced by Kf".

Find [Ca2+] in 0.10 M CaY2- at pH 8.00

Pyrocatechol violet(Table 12-3) is to be used as a metal ion indicator in an EDTA titration. The procedure is as follows:

1. Add a known excess of EDTA to the unknown metal ion.

2. Adjust the pH with a suitable buffer.

3. Back-titrate the excess chelate with standard Al3+.

From the following available buffers, select the best buffer, and then state what color change will be observed at the end point. Explain your answer.

  1. pH 6–7 (ii) pH 7–8 (iii) pH 8–9 (iv) pH 9–10

A 50.0-mL sample containing Ni2+ was treated with 25.0 mL of 0.050 0 M EDTA to complex all the Ni2+ and leave excess EDTA in solution. The excess EDTA was then back-titrated, requiring 5.00 mL of 0.050 0 M Zn2+. What was the concentration of Ni2+ in the original solution?
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