Relative molecular mass is the average mass of one molecule of a substance compared to the mass of 1/12 of a carbon-12 atom.
Month: August 2020
Define relative atomic mass.
Relative atomic mass is the average mass of one atom of an element compared to the mass of 1/12 of a carbon-12 atom.
Write down the 3 formulas to find the number of moles of a substance.
No. of moles = Mass/ Mr or Mass/ Ar
No. of moles = Volume (dm3) x Concentration (mol/dm3)
No. of moles = Volume (dm3) / 24 dm3
Explain, using structure and bonding, why ethanol cannot conduct electricity.
Ethanol has a simple covalent structure. It exists as discrete molecules in the different states. There are no mobile ions or delocalised electrons to conduct electricity.
Running Distance and Time
ratio m:n:p
Double-Pivot Push-up
Why is there a need to recycle metals?
Metals are finite resources.
With the increasing demand for metals, our metal reserves will not last much longer.
Hence, there is a need to recycle metals to conserve the metal resources.
Recycling metals also use up less energy and produce fewer pollutants than extracting metals from their ores.
What are the observations when Group I metals react with cold water?
– Metal piece darts about quickly around the surface of the water
– Effervescence observed (due to hydrogen gas produced in water)
– Hissing sound heard (due to the vigorous release of hydrogen gas)
– Metal piece becomes smaller in size
– Flame observed (for some metals)
– Lithium (no flame)
– Sodium (yellow flame)
– Potassium (lilac flame)
– pH of solution increases from pH7 to pH14 (due to the formation of a strong alkali)
Describe the effects of absorbing electromagnetic waves.
Heating Effect
– Infrared heating
Fires and hot bodies emit infra-red radiation. Our skin absorbs the infra-red rays, making us feel warm.
– Microwaves heating
Microwaves are of a non-ionizing character. However, microwaves, being more penetrative, can cause more severe burns to the skin, especially when skin has high water content.
Ionisation Effect
UV rays, X-ray, Gamma ray can cause breakdown of DNA, and ionization of molecules and atoms in living matter. The mutation of these cells and atoms can lead to formation of cancerous cells.