Unit 1-Acids & Bases Topic 7
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• What does the pH of a substance tell you? • What range of numbers does the pH scale span?
• How acidic or alkaline a substance is (the pH of the substance) • pH scale is continuous range that stretches from below 0 to above 14. Most common pH values occur between 0 and 14.
What word is used to describe chemical with a pH of a. Less than 7 b. exactly 7 c. More than 7
a. Acids have a pH of less than 7. b. Water and neutral solutions have a pH of exactly 7. c. Alkalis have a pH more than 7.
What is the difference between a base and an alkali?
Substances that can react with acids and neutralise them to make a salt and water are called bases. Bases that dissolve in water are called alkalis.
How are acids and alkalis formed?
An alkaline solution can be formed when a metal oxide is dissolved in water. An acidic solution can be formed when a non-metal oxide is dissolved in water.
The data booklet has a table of solubilities on page 8. What type of chemicals would have no effect on pH?
Insoluble substances will have no effect on pH.
Acidic and alkaline solutions can conduct electricity because they have ions that are free to carry charge. What ion do all acids contain?
Hydrogen ion H+
Which acids are the following formulae representing? i) HCl or H+ (aq)Cl-(aq) ii) H2SO4 or 2H+(aq) SO42-(aq) iii) HNO3 or H+(aq) NO3<span>-</span>(aq)
i) Hydrochloric acid ii) Sulphuric acid iii) Nitric acid
Acidic and alkaline solutions can conduct electricity because they have ions that are free to carry charge. What ion do all alkalis contain?
Hydroxide ion OH<span>-</span>
Which alkalis are the following formulae representing? i) NaOH or Na+ (aq) OH-(aq) ii) Ca(OH)2 or Ca+(aq) 2OH-(aq) iii) LiOH or Li+(aq) OH-(aq)
i) Sodium hydroxide ii) Calcium hydroxide iii) Lithium hydroxide
Describe how the concentration of H+ ions and pH changes when an acid is diluted.
When an acid is diluted the concentration of H+ ions is decreased and the pH increases towards 7.
Describe how the concentration of OH- ions and pH changes when an alkali is diluted.
When an alkali is diluted the concentration of OH- ions is decreased and the pH decreases towards 7.
Water is a covalent compound. These do not conduct electricity. Yet I was always told not to make toast in the bath. Please explain.
No one likes soggy toast. A very small proportion of water molecules will dissociate into an equal number of hydrogen and hydroxide ions. H2O(l) ⇔ H+(aq) + OH-(aq)
How does the concentration of hydrogen ions (H+(aq)) compare to the concentration of hydroxide ions (OH-(aq)) in water and neutral solutions?
In water and neutral solutions, the concentration of hydrogen ions (H+(aq)) is equal to the concentration of hydroxide ions (OH-(aq)) .
How does the concentration of hydrogen ions (H+(aq)) compare to the concentration of hydroxide ions (OH-(aq)) in an alkaline solution,
In alkaline solutions, the concentration of hydroxide ions (OH-(aq) is greater than the hydrogen ion (H+(aq)) concentration.
How does the concentration of hydrogen ions (H+(aq)) compare to the concentration of hydroxide ions (OH-(aq)) in an acidic solution.
In acidic solutions, the concentration of hydrogen ions (H+(aq)) is greater than the hydroxide ion (OH-(aq)) concentration.