Properties of acids
- Weak acids have a sour taste
- Acids change the colour of indicators such as phenolphthalein, litmus and universal indicator.
- Acids react with certain metals to form hydrogen gas (zinc, magnesium, aluminium ,iron and other reactive metals but not copper) and a salt
- Acids react with carbonates and hydogen carbonates (old fashioned name bicarbonates)
- Acids react with bases or alkalis to form a salt and water.
- Acids release hydrogen ions when they are dissolved in water.
Properties of Bases and Alkalis
All metal oxides and hydroxides are bases. Metal oxides don’t dissolve in water. Sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonium hydroxide dissolve in water. Bases like these that dissolve in water are called alkalis.
Most household cleaning products contain contain bases. Oven cleaners contain sodium hydroxide (sometimes called caustic soda). Sodium hydroxide reacts with fat and grease to break them down. Soap is made when sodium hydroxide reacts with fats or oils.
Sodlum hydroxide feels soapy to touch because it reacts with fat and oil in your skin
Toothpaste contains a weak base to neutralise the acid produced by mouth bacteria.
Antacid tablets contain carbonates to react with and neutralise excess acid in the stomach.
- Weak bases have a bitter taste and feel slippery to touch.
- Bases change the colour of indicators (litmus phenolphthalein and universal indicator)
- Bases react with acids to form a salt and water
- Soluble bases (Alkalis) release hydroxide ions in solution)
Homework
Watch the video about using universal indicator to test the pH of different solutions. Watch also how the pH changes during a neutralisation reaction.
Answer the questions after it. To be handed in on Tuesday…..have a good weekend.
- why should you wear gloves when using Mr Muscle?
- What pH would you predict for toothpaste? What colour would universal indicator turn when it is used to test the pH of toothpaste?
- What colour is phenolphtalein in acid solution?
- What colour is phenolphthalein in basic solution
- What colour does universal indicator turn when it is added to vinegar? What is the pH of vinegar?
- What colour does universal indicator turn when it is added to Mr Muscle. What is the pH of Mr Muscle?
- What colour does universal indicator turn when it is added to baking soda (sodium hydrogen carbonate) in solution. What is the pH of baking soda solution?
- What colour does universal indicator turn when it is added to lemon juice. What is the pH of lemon juice?
- What colour does universal indicator turn when it is added to a solution of table salt. What is the pH of salt solution? Why does salt solution have this pH?
- What is the PH of sodium hydroxide solution. Is it a strong or weak base?
- What is the pH of hydrochloric acid solution? Is it a strong or weak acid?
- When vinegar is neutralised with sodium hydroxide the hydrogen ions are removed and the pH of the solution changes till it reaches a pH of 7 (completely neutral) Describe the colour changes you would see when vinegar is neutralised with sodium hydroxide solution. (Use the colours from the colour chart.
- Writing fully balanced chemically equations.
………but first a reminder about salts and word equations
When hydrochloric acid reacts with a base and is neutralised salts known as chlorides are produced.
When sulphuric acid reacts with a base and is neutralised salys known as sulphates are produced.
When nitric acid reacts with a base and is neutralised salts known as nitrates are produced.
Here are the general word equations for reactions you need to know about.
acid + base —-> salt + water (bases are metal oxides and hydroxides)
acid + carbonate —–> salt + carbon dioxide + water
acid + hydrogen carbonate —–> salt + carbon dioxide + water
acid + metal —-> salt + hydrogen
Now complete each word equation, write down the chemical formulae and finish with a fully balanced chemical equation.
copper oxide + nitric acid —->
sodium hydroxide + sulphuric acid —->
calcium carbonate + hydrochloric acid —->
magnesium + hydrochloric acid
hydrochloric + sodium hydrogen carbonate —->
Use the table of ions from your text book to help write chemical formulae