1.8 Acids, bases and salts Flashcards
What are indicators?
Indicators are dyes that come from plants that change colour in acids and alkalis.
Describe the colours that different indicators go in acidic, neutral and alkaline solutions?
-Litmus is red in acid, purple neutral and blue in alkaline solutions.
-Methyl Orange is red in acid, orange in neutral and yellow in alkaline solutions.
Phenolphthalein is colourless in acid and neutral solutions and pink in alkalis.
-Red litmus paper turns blue in alkalis but stays red in neutral or acidic solutions.
-Blue litmus paper turns red in acids but stays blue in neutral or alkaline solutions.
Why do we use Universal Indicator?
To distinguish between strong and weak acids and alkalis.
Explain the pH scale and give examples of each pH range
-Strong acids have a pH of 0-2 (red) e.g. hydrochloric, sulfuric and nitric acid.
-Weak acids have a pH of 3-6 (orange or yellow) e.g. ethanoic and carbonic acid.
-Neutral solutions have a pH of 7 (green) - water.
-Weak alkalis have a pH of 8-11 (blue or indigo) e.g. ammonia.
-Strong alkalis have a pH of 12-14 (violet) e.g. sodium and potassium hydroxide.
What are the properties of acids?
-Acids have a sour taste, e.g. vinegar and lemon juice.
-They turn litmus red.
-They have a pH < 7.
-They dissolve in water producing hydrogen ions in solution: H+ (aq).
The greater the concentration of these hydrogen ions, the greater the acidity/ lower pH.
What is the difference between a strong and weak acid?
-Strong acids are completely ionised in water; this means they break up completely into ions and there is a high concentration of hydrogen ions in the solution.
-Weak acids are partially ionised in water. This means only a small fraction of the molecules break into ions when added to water.
What is the difference between a concentrated and dilute acid?
A concentrated acid contains a large number of hydrogen ions dissolved per unit volume.
A dilute acid contains a small number of hydrogen ions dissolved per unit volume.
Concentration is measured in moles per cubic decimetre (mol/dm3). One decimetre cubed (dm3) is 1000cm3.
What is the difference between strong and weak alkalis?
Strong alkalis are completely ionised in water; this means they break up completely into ions e.g. NaOH and KOH.
Weak alkalis are partially ionised in water; this means they do not break up into ions in water, and so there are fewer hydroxide ions in solution e.g. ammonia solution.
What is the ion present in acid and alkalis?
Acid - H+ (aq)
Alkalis - OH- (aq)
What is the most and least reactive metal towards acids from the experiment?
Magnesium (most) and copper (least).
Which acid reacts more slowly: sulfuric or ethanoic?
Ethanoic acid reacts more slowly because it is a weak acid and so only partly ionises in water. This means it releases fewer hydrogen ions, H+ (aq), into the solution. It is the hydrogen ions that react with the metals.
What are the observations common to all the reactions that take place between a metal and acid?
-Bubbles of gas (hydrogen); and heat released.
-Metal reacts and get smaller and may disappear.
-Forms a clear solution (some of the salt solutions may be coloured).
Why do you not react group 1 metals with acid?
These metals are too high in the reactivity series and would react dangerously with the acids, probably exploding on contact.
What is the definition of a salt?
A salt is a compound formed when some or all of the hydrogen ions in an acid are replaced by metal ions or the ammonium ion.
What is the general equation for the reaction of a metal with an acid?
Metal + acid —> Metal salt + Hydrogen (MASH)
