Explain the formation of scum when hard water is treated with soap.
Soap does not work properly in hard water. A soap is a sodium or potassium salt of long chain carboxylic acid. Hard water contains salts of calcium and magnesium. When soap is added to hard water, sodium and potassium ions present in soap displace calcium or magnesium ions from the water molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.
For example:
Sodium Stearate + Calcium chloride → Sodium chloride + Calcium Stearate (scum)
Formation of scum hinders the formation of foam, so soap is thus unable to clean in hard water.
Draw the structure for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal.
*Are structural isomers possible for bromopentane?
What is an homologous series? Explain with an example.
How would you name the following compounds?
(i) CH3 -- CH2 -- Br
(ii)
(iii)
What will be the formula and electron dot structure of cyclopentane?
Explain the nature of the covalent bond using the bond formation in CH3Cl.
Why are carbon and its compounds used as fuels for most applications?
How many structural isomers can you draw for pentane?
Explain the mechanism of the cleaning action of soaps.
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
How would you distinguish experimentally between an alcohol and a carboxylic acid?
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the difference between a reflex action and walking?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Why should a magnesium ribbon be cleared before burning in air?
Define the principal focus of a concave mirror.
How does chemical coordination take place in animals?
What is geothermal energy?
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south (b) towards east
(c) downward (d) upward
Outline a project which aims to find the dominant coat colour in dogs.
How do auxins promote the growth of a tendril around a support?
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
How does the creation of variations in a species promote survival?
When does an electric short circuit occur?
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?