PLACING OF 'USED'

Before a noun

When 'used' is placed before a noun as an adjective, it generally means 'second-hand' (used by someone else).

e.g. This garage sells used cars.

"Good quality used toys are also very welcome." (Article in The Bolton News)

After a noun

e.g. All chemicals used were of analytical grade.

The above sentence is found in many scientific papers. It means that all the chemicals that were used in a particular experiment or series of experiments were of analytical grade. In this context, 'used' should always be placed after the noun.

All used chemicals were of analytical grade.

Placing 'used' before the noun implies that the chemicals are 'second-hand'. Although this grammatically incorrect phrase has crept into some published papers, 98% of papers containing this phrase (according to Google Scholar) place 'used' after the noun.

CONTRACTIONS

A contraction is "a shortening of a word or group of words" (Collins English Dictionary). Usually, the missing letters are replaced by an apostrophe.

For example:

cannot → can't

does not → doesn't
we will → we'll
would not → wouldn't

Contractions can be used in informal writing or in conversation. When used in conversation, they help to make speech sound more natural.

Contractions are generally not considered acceptable in formal writing, such as academic papers or job applications. In formal writing, words and phrases should be written out in full.

BEWARE OF THE THESAURUS!

A piece of writing can be dull if adjectives are used repeatedly. We can use a thesaurus to add variation to our writing; however, this should be used with caution as no two words have exactly the same meaning.

Here's an example; you are writing a scientific paper and you want to describe the performance of a catalyst. You want to find an alternative to 'good' and 'excellent' because you have used those words a few times already.

You get out your thesaurus (or access one online) and discover that 'distinguished' is a synonym of 'excellent', so you write,

"X gives a distinguished performance as a catalyst for . . . "

Unfortunately, this is not quite right. As an adjective, 'distinguished' is normally used to describe people. The Collins online dictionary defines 'distinguished' as,

1. noble or dignified in appearance or behaviour
2. eminent; famous; celebrated

http://www.collinsdictionary.com/dictionary/english/distinguished

A good strategy is to use a dictionary in combination with a thesaurus to make sure that a word is suitable for your purpose. Using Google to see how words are used in sentences can also be helpful.