UKPCS Science Chemistry: pH,neutral solution,carbonates #43

Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science Chemistry (paper 6). 

  • pH
    • pH (potential of hydrogen) is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is.
    • More acidic solutions, have lower pH. More alkaline solutions, have higher pH. Substances that aren’t acidic or alkaline (that is, neutral solutions) usually have a pH of 7.
    • Acids have a pH that is less than 7. Alkalis have a pH that is greater than 7.pH is a measure of the concentration of protons (H+) in a solution.
    • Typical indicators are phenolphthalein, methyl orange, methyl red, bromothymol blue, and thymol blue. They each change colour at different points on the pH scale, and can be used together as a universal indicator.
    • Another way is to use litmus paper, which is based on a natural pH indicators.

  • Neutral solutions

Neutral solutions have a pH of 7. They do not change the colour of litmus paper, but they turn universal indicator green. Water is neutral.

  • Carbonates

When acids react with carbonates, such as calcium carbonate (found in chalk, limestone and marble), a salt, water and carbon dioxide are made. In general:

acid + metal carbonate → salt + water + carbon dioxide

Notice that an extra product – carbon dioxide – is made. It causes bubbling during the reaction, and can be detected using limewater. You usually see this reaction if you study the effects of acid rain on rocks and building materials.

  • Reactive metals

Acids will react with reactive metals, such as magnesium and zinc, to make a saltand hydrogen. In general:

acid + metal → salt + hydrogen

The hydrogen causes bubbling during the reaction, and can be detected using a lighted splint. You usually see this reaction if you study the reactivity series of metals.



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