Acids, Alkalis and Salts

Question 1

Describe the use of the indicators litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions

Answer 1

Litmus paper is red in acidic solutions and blue in alkali
Phenolphthalein is colourless in acid and pink in alkali
Methyl Orange is red in acidic and yellow in alkali

Question 2

What is the pH scale?

Answer 2

The pH scale ranges from 0-14 and tells you how acidic or alkali a solution is. 0 is strongly acidic, 7 is neutral and 14 is strongly alkaline

Question 3

Describe the use of universal indicator to measure the approximate pH value of a solution

Answer 3

Changes through a variety of colours from 1 to 14 and the colour is checked against a chart to tell you how acidic or alkaline a solution is

Question 4

How do you define acids and alkalis?

Answer 4

Acids are hydrogen ions, H+

Alkalis are hydroxide ions, OH-

Question 5

Predict the products of reactions between dilute hydrochloric, nitric and sulfuric acids; and metals, metal oxides and metal carbonates (excluding the reactions between nitric acid and metals)

Answer 5

Hydrochloric acid = chlorides
Nitric acid = nitrates
Sulfuric acid = sulfates

For metals:
Metal + acid -----> salt + hydrogen
For Metal oxides: 
Metal Oxide + acid -----> salt + water
For metal carbonates:
Metal carbonate + acid -----> salt + carbon dioxide + water

Question 6

What are the general rules for predicting the solubility of salts in water?

Answer 6

All common sodium, potassium and ammonium salts are soluble
All nitrates are soluble
Common chlorides are soluble, except silver chloride
Common sulfates are soluble, except those of barium and calcium
Common carbonates are insoluble, except those of sodium, potassium and ammonium

Question 7

Describe experiments to prepare soluble salts from acids

Answer 7

Use an excess of the base so all the acid is used up
Unused base is filtered off and the solution is concentrated by boiling. it until crystals form on cooling
Solution is left to from crystals
Any uncrystallised solution can be poured off the crystals

Question 8

Describe experiments to prepare insoluble salts using precipitation reactions

Answer 8

Mix two solutions, one with positive ions, the other negative
The mixture is filtered to get the precipitate
Wash it on the filter paper and leave to dry

Question 9

Describe experiments to carry out acid-alkali titrations

Answer 9

Add 25cm3 of alkali to a conical flask using a pipette and add a few drops of Methyl Orange indicator.
Add and acid in the burette until the indicator turns from yellow to orange.
The volume to acid is noted and the same volume of acid and alkali are mixed together in a conical flask without any indicator
The solution can be crystallised by evaporation to the point that crystals form on cooling and then leave it to form crystals. Crystals are separated form the remaining solution and left to dry.
FOR NaCl evaporate solution because NaCL crystals don’t contain water of crystallisation