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Properties of Acids and Bases are many, including different tastes, types and characteristics. Some of the properties include:
- Acids are referred to as chemical substances characterized by a sour taste in an aqueous medium.
- Bases can be defined as chemical substances which are characterized by a bitter taste and are slippery to the touch.
- Some bases are soluble in water while others are not.
- Acids are chemical substances that when dissolved in water dissociate into hydrogen (H) ions, while bases are substances that when added to water release hydroxide (OH) ions.
Both Acids and Bases have their properties divided into two categories:
- Physical properties
- Chemical Properties
Read Also: Importance of pH in Everyday Life
| Table of Content |
Key Terms: Acids, Bases, Hydroxides, Sulphuric Acid, Benzoic Acid, Hydrogen Ions, Metal Oxide, HNO3, Hydroxide Ions
What are Acids?
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Acid is a term first derived from the Latin word “Acidus” or “Acere” which means sour. Acids are known for their sour taste. Acids can be defined as:
| “Any substance that has hydrogen and is able to donate a proton (hydrogen ion) to another substance.” |
- Acid is a substance which yields ionizable ion (H3O+) in its aqueous solution.
- Acids turn blue litmus paper into red.
- It dissociates in its aqueous solution to form constituent ions.
The same can be shown by the following examples:
- HCl (aq) → H+ + Cl-
- H2SO4 → 2H+ + SO4-2
- CH3CO2H (aq) → H+ + CH3CO2-
What are Bases?
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Bases can be defined as:
| “Any molecule or ion which is known to accept hydrogen ions from an acid.” |
- Bases are known for their bitter taste and slippery texture.
- A base which can be dissolved in water is an alkali.
- When bases react with acids, they produce salts.
- Bases turn red litmus blue.
Read Also: The Alkali Metals
Physical Properties of Acids and Bases
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The physical properties of acids and bases are given below:
| Properties | Acids | Bases |
|---|---|---|
| Colour | Mineral acids are colourless liquids. However, sulphuric acid becomes yellow since there are impurities. Some organic acids are coloured white solids. Examples: Benzoic Acid | Bases are colourless in nature. The same is not applicable for the hydroxides of iron and copper. |
| Taste | Sour | Bitter |
| Touch | Wet | Slippery |
| Solubility in Water | Soluble | Some bases are soluble |
Physical Properties of Acid
The litmus test was one of the physical properties that we had discussed at the very beginning of the topic. The other physical properties are taste, colour, solubility, and corrosiveness.
- Taste: All acids taste sour.
- Solubility: Almost all acids are soluble in water.
- Corrosiveness: Most of the acids are corrosive in nature.
Also Read:
| Related Links | ||
|---|---|---|
| Concentration of Ore | Inner Transition Metals | Red Phosphorus |
| Polymerization | Actinoids | Electrolytic Cell |
| Salt Analysis | Ammonium phosphate | Sulfuric Acid (H2SO4) |
Chemical Properties of Acids and Bases
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There are several chemical properties of acids and bases:
Reactions of Acids and Bases with metals
Metals generally displace hydrogen from the acids when react with an acid. This results in the evolution of hydrogen gas. The metals combine with the remaining part of acids to form a salt. For example, the reaction of sulphuric acid with zinc.
Example:
2HCl (aq. soln) + Mg → MgCl2 (Magnesium chloride) + H2 (g)
2NaOH (aq. soln) + Zn → Na2ZnO2 (Sodium zincate) + H2 (g)
Reactions with Metal Carbonates/Bicarbonates with Acids
Metal carbonates/metal bicarbonates react with acids in order to produce salt, carbon dioxide and water. For example the reaction of sodium carbonate or sodium bicarbonate with hydrochloric acid.
Equation: Acid + Carbonate → Salt + Water + Carbon dioxide
Example: H2SO4 (aq. soln) + CuCO3 → CuSO4 + H2O + CO2 (g)
Reaction of Metal Oxide with Acids
Metal oxides react with acids in order to produce salt and water. For example, the reaction of copper oxide and dilute hydrochloric acid.
Equation: CuO + 2HCl → CuCl2 + H2
Reaction of Non-metal Oxides with Bases
Non-metal oxides react with bases in order to produce salt and water. For example the reaction of carbon dioxide and lime water (calcium hydroxide)
Example:
HCl + H2O → H3O+ + Cl-
H+ + H2O → H3O+
Neutralization of Acid and Base
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Neutralization is the reaction between an acid and a base that invariably produces salt and water. In a neutralization reaction, one H+ ion of acid is neutralized by one OH– ion of base.
And complete neutralization takes place when all the H+ ions in the acidic solution are neutralized by the same number of OH– ions of the basic solution. The relative amounts of acid and base required for complete neutralization is based on the total number of H+ and OH– ions produced by the respective acid and base.
Properties of Acids and Bases Comparative Study
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The comparative study of the properties of acids and bases include:
- All acids and some of the alkalies are known to show corrosive action on the skin. This is because they form blisters when in contact with the skin.
- H2SO4 is found to absorb water from the tissues of the skin. Similarly, Nitric Acid or HNO3 forms a pulp-like mass because it reacts with skin proteins. NaOH and KOH are known as caustic soda and caustic potash respectively because they cause a causticizing action on the skin.
- Every acid reacts with alkalis (metal hydroxides) in order to form salt and water. Here, Neutralization occurs when there is a reaction between acid and base in order to form salt and water as its resulting products.
Thus, the reactions that occur are:
- 2KOH + H2SO4 → K2SO4 + 2H2O
- Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O
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Things to Remember
- Acids are chemical substances distinguished by a sour taste in an aqueous medium.
- On the other hand, bases can be defined as chemical substances which are characterized by a bitter taste and are slippery to the touch.
- The word “acid” is derived from the Latin word for sour. This distinguishable property helps identify acids from other compounds like salt and bases.
- Many acids out there can be hazardous if ingested and shouldn’t be tasted.
- Acids become a neutral substance once the acid binds to the base. Often this reaction can lead to water and salt. This is often seen when strong acids react with strong bases.
- The acids are driving electricity. Apart from this, the batteries are used to produce electricity. The acid that conducts electricity strongly is a strong acid, and the acid that conducts electricity weakly is basically a weak acid.
Sample Questions
Ques: Name the uses of acids? (1 mark)
Ans: Some of the uses of acids are:
- Acids are used to store milk.
- HCl is used to clean sanitary ware.
- Nitric Acid is used for the cleaning of gold jewellery.
Ques: Give two acid examples? (1 mark)
Ans: Acids are liquids that are the concentration of hydrogen ions. There are many common acid examples: lemon juice (citric acid), vinegar (acetic acid), stomach acid, and soda pop (carbonic acid). Acids are typically ionic with a positive hydrogen ion attached to a negative anion.
Ques: What is acid base and salt with example? (1 mark)
Ans: The reaction of acid and base produce two products; water and an ionic compound which is salt. This type of reaction is called a neutralization reaction. For instance, sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
Ques: How are the basic salts formed? (1 mark)
Ans: Basic salts are formed by the process of neutralization of a strong base and weak acid; for instance, the reaction of sodium hydroxide (a strong base) with acetic acid (a weak acid) produces water and sodium acetate. The conjugate acid of the low base makes the salt acidic.
Ques: Write the properties of an acid? (3 marks)
Ans: Some properties of acids are:
- When dissolved in water, acids conduct electricity, taste acidic and react with metals to create hydrogen gas.
- Some indicator compounds can be used to detect acids, such as litmus.
- Acids turn blue litmus paper into red.
- Acid strength is measured on a pH scale.
Ques: What are examples of acids? (1 mark)
Ans: Acids are substances in solution which produce Hydrogen ions. Acids, while releasing hydrogen gas, are corrosive to metals, have a pH between 0 and 6.9, and are sour to taste. Acids are found in many substances: lemon juice (citric acid), vinegar (acetic acid), stomach acid, and soda pop (carbonic acid).
Ques: Is it possible that acids can react with metals? (2 marks)
Ans: Acids are known to react with metals in order to form salt and release hydrogen gas.
Thus, one instance can be represented as:
2 M + 2 HX → 2 MX + H2
Ques: A sodium hydroxide solution of 2 mL has been added to a couple of pieces of granulated zinc metal which is taken in a test tube. When warmed, a gas rises, and bubbled through a soap solution prior to testing. Thus, what is the equation involved and the test to detect the gas? What is the name of the gas that rises when the same metal has been seen to react with a dilute solution of a strong acid? (4 marks)
Ans: Active metals, such as zinc react with strong bases including NaOH, KOH etc. in order to release hydrogen gas and salt.
Thus,
2NaOH (aq) (sodium hydroxide) → Na2ZnO2 (aq) (sodium zincate salt) + H2 (g)
The release of gas can be seen by the bubble formation in the soap solution.
Then, there is a test to detect H2 gas:
When a flaming matchstick is placed on the mouth of this test tube, a pop sound can be heard, confirming that there is H2 gas. H2 is released when Zn metal reacts with a dilute solution of strong acid.
Thus,
Zn + 2HCl (Strong acid) → ZnCl2 (Salt) + H2\(\uparrow\) (Gas)
Ques: Balance the given chemical equations: (3 marks)
(i) HCl(aq) + H2O(l) →
(ii) CaCO3(s) + H2O(l) + CO2(g) →
(iii) NaOH(aq) + Zn(s) →
Ans: The reactions that occur are:
(i) HCl(aq) + H2Ol > H3O+ Cl–(aq)
(ii) CaCO3(s) + CO2(g) + H2Ol → Ca(HCO3)2(aq)
(iii) 2NaOH(aq) + Zn(s) → Na2ZnO2(aq) + H2(g)
Explain these substances in terms of chemical reactions that dissociate to produce ions in their solutions.
(i) Hydrochloric acid
(ii) Nitric acid
(iii) Sulphuric acid
(iv) Sodium hydroxide
(v) Potassium hydroxide
(vi) Magnesium hydroxide (CBSE Boards Term 1, 2017) (5 marks)
Ans: Dissociation of substances in order to produce ions in their solutions include:
(i) Hydrochloric acid (HCl):
HCl(aq) ⇌ H+(aq) + Cl–(aq)
(ii) Nitric acid (HNO3
HNO3(aq) ⇌ + H+aq + NO–3(aq)
(iii) Sulphuric acid (H2SO4):
H2SO4(aq) ⇌ 2H+(aq) + SO2-4(aq)
(iv) Sodium hydroxide (NaOH):
NaOH(aq) ⇌ Na+(aq) + OH–(aq)
(v) Potassium hydroxide (KOH) :
KOH(aq)⇌ K+(aq) + OH–(aq)
(vi) Magnesium hydroxide [Mg(OH)2] :
Mg(OH)2(aq) ⇌ Mg2++(aq) + 2OH– (aq)
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