June exam

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Properties of acids

Acids are a class of chemical compounds that exhibit certain properties. The most common ones are:

• Sour taste: Many acids, such as citric acid or acetic acids in vinegar, have a ^^sour taste^^. It’s important to note that tasting acids can be detrimental to one’s health.
• pH less than 7: Acids have a ^^pH value less than 7^^ on the pH scale. The lower the pH value, the stronger the acid.
• Reactivity with metals: Acids have the ^^ability to react with certain metals^^, such as zinc or magnesium, to ^^produce hydrogen gas and a salt^^.
• Corrosive nature: Acids are ^^corrosive substances^^ that can cause damage to various materials.
• Conductivity: Most acids are ^^electrolytes^^, meaning they ^^can conduct electricity^^.
• Turns blue litmus paper red: Acids have the ability to ^^change the colour of blue litmus paper to red^^.
• Reactivity with bases: Acids ^^react with bases^^ to ^^form salts and water^^ in a chemical reaction known as ^^neutralisation^^.
• Sour-smelling gases: Some acids ^^release sour-smelling gases^^ when they react with certain substances.

Reaction of acids with metals

When ^^acids react with metals^^, they typically ^^produce salt and hydrogen gas^^. The general equation for the reaction between an acid and a metal is:

^^Acid + Metal → Salt + Hydrogen Gas^^

Here are some examples of specific reactions between acids and metals:

• Hydrochloric acid (HCl) with zinc (Zn): 2HCl + Zn → ZnCl2 + H2
  • Hydrochlori acid reacts with zinc to produce zinc chloride (a salt) and hydrogen.
• Nitric acid (HNO3) with magnesium (Mg): 2HNO3 + Mg → Mg(NO3)2 + H2
  • Nitric acid reacts with magnesium metal to produce magnesium nitrate (a salt) and hydrogen.

Reactions of acids with bases

When ^^acids react with bases^^, they undergo a chemical reaction called ^^neutralisation^^. In this reaction, the acidic and basic properties of the substances neutralise each other, resulting in the formation of ^^salt and water^^. The general equation for the reaction between an acid and a base is:

^^Acid + Base → Salt + Water^^

Here are some examples of specific reactions between acids and metals:

• Hydrochloric acid (HCl) with sodium hydroxide (NaOH): HCl + NaOH → NaCl + H2O
  • Hydrochloric acid reacts with sodium hydroxide to produce sodium chloride (salt) and water.
• Sulfuric acid (H2SO4) with potassium hydroxide (KOH): H2SO4 + 2KOH → K2SO4 + 2H2O
  • Sulfuric acid reacts with potassium hydroxide to produce potassium sulfate (salt) and water.

Reactions of acids with carbonates

When ^^acids react with carbonates^^, they ^^produce salt, water and carbon dioxide^^. This type of reaction is commonly known as an ^^acid-carbonate reaction^^. The general equation for the reaction between an acid and a carbonate is:

^^Acid + Carbonate → Salt + Water + Carbon Dioxide^^

Here are a few examples of specific reactions between acids and carbonates:

• Hydrochloric acid (HCl) with calcium carbonate (CaCO3): 2HCl + CaCO3 → CaCl2 + H2O + CO2
  • Hydrochloric acid reacts with calcium carbonate to produce calcium chloride (salt), water, and carbon dioxide.
• Sulfuric acid (H2SO4) with sodium carbonate (Na2CO3): H2SO4 + Na2CO3 → Na2SO4 + H2O + CO2
  • Sulfuric acid reacts with sodium carbonate to produce sodium sulfate (salt), water and carbon dioxide

Balancing equations

Balancing the equation for the reaction between hydrogen (H2) and oxygen (O2) to form water (H2O).

H2 + O2 → H2O

1. ^^Count the number of atoms^^ for each element on both sides of the equation

On the left side:

• 2 hydrogen atoms
• 2 oxygen atoms

On the right side:

• 2 hydrogen atoms
• 1 oxygen atom

2. ^^Begin by balancing the elements^^ that appear in the fewest compounds

3. Balance the oxygen atoms by ^^adding a coefficient in front^^ of the water molecule

• H2 + O2 → 2H2O

  Now the oxygen atoms are balanced, but the hydrogen atoms are unbalanced.

4. Balance the hydrogen atoms by adjusting the coefficient in front of the hydrogen molecule

• 2H2 + O2 → 2H2O

  Now the hydrogen atoms are also balanced, with 4 atoms on both sides.

The balanced equation for the reaction is : 2H2 + O2 → 2H2O

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Acid rain

Acid rain refers to precipitation that has a pH level lower than the average pH of rainwater, which is around 5.6. It is primarily caused by the ^^emission of certain pollutants into the atmosphere^^, especially ^^sulphur dioxide^^ (SO2) and ^^nitrogen oxide^^ (NO), which ^^react with water, oxygen^^ and other compounds in the air to ^^form various acidic substances^^.

Formation of acid rain

1. Emission of pollutants: ^^Industrial activities^^, such as burning fossil fuels in power plants in power plants, factories and vehicles, ^^release sulphur dioxide and nitrogen oxide^^ into the air. These pollutants are often ^^produced by the combustion of coal, oil and gas.^^
2. Atmospheric reactions: Once in the atmosphere, sulphur dioxide and nitrogen oxide ^^undergo complex chemical reactions^^ with oxygen, water vapour, and other chemicals. They can form sulphuric acid (H2SO4) and nitric acid (NNO3), which are highly acidic.
3. Precipitation: These acidic compounds, along with the water vapour eventually ^^condense and form acid rain^^, snow, fog or dew. When these acidic forms of precipitation fall to the ground, they can have harmful effects on the environment.

Effects of acid rain

• Environmental impact: Acid rain has ^^detrimental effects on forests, lakes, rivers and other aquatic ecosystems^^. It can ^^damage plant life^^, degrade soil quality and contribute to the acidification of bodiest of water, which affects fish and other aquatic organisms.
• Corrosion and damage to buildings and infraestructure: ^^Acid rain can corrode metals^^ such as iron and steel, and cause damage to buildings, bridges or other structures.
• Impact on human health: Whilst the direct ^^effects of acid rain on human health are relatively minimal^^, the pollutants associated with acid rain (sulfur dioxide and nitrogen oxide) can ^^contribute to the formation of fine particulate matter^^ (PM2.5) and ground-level ozone. These pollutants can have ^^adverse effects on our respiratory system^^ and worsen air quality.

Objects that are affected by acid rain

• Iron (steel) bridges
• Marble statues
• Plastic containers
• Aquatic animals
• Space stations

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