Fatty acid with only single covalent bonds is said to be

These are known to be saturated.  
The definition of a saturated fatty acid is that the carbon chain coming off of the acid group contains only single bonds.  An unsaturated fatty acid contains at least one double bond in the carbon chain coming off of the acid group.  Saturated fats are usually fats (solid at room temperature) while unsaturated fats can be oils (liquid at room temperature) this is because the single bonds in the saturated fats give the molecule a shape that can stack on another saturated fat molecule more easily which makes the melting points higher.  The double bonds (usually referring to cis double bonds since trans double bonds are in trans fats) in unsaturated fats give the molecule a shape that cannot stack on another unsaturated fat molecule easily which makes the melting point lower.

I hope this helps.  Please let me know if anything is unclear or if you want further explanation.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.