Metals and Non-Metals — Science STD 10 — Question

How were the positions of isotopes of an element decided in the modern periodic table?

Why does ethyne (acetylene) burn with a sooty flame?

A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Sea water contains many salts dissolved in it. How can the salt that we use in food is obtained?

Explain why, though aluminium is more reactive than iron, yet there is less corrosion of aluminium when both are exposed to air.

Name two ores of zinc. Write the names of the chemical compounds present in them and give their chemical formulae.

What is meant by strong acids and weak acids? Classify the following into strong acids and weak acids:
HCl, CH₃ COOH, H₂SO₄, HNO₃, H₂CO, H₂SO₃

An element A has 4 valence electrons in its atom whereas element B has only one valence electron in its atom. The compound formed by A and B does not conduct electricity. What is the nature of chemical bond in the compound formed? Give its electron-dot structure.

How does the atomic size vary on going down from top to bottom in a group of the periodic table? Why does it vary this way?

Why Al metal cannot be obtained by the reduction of Al₂O₃ with coke? Explain.