How to solve these questions in Chemistry?

Question

How do you solve this one question in Chemistry?

1. The solubility of salt ar 25°C is about 385 g/L. If the temperature is raised to 50°C, then:
_______ more salt would dissolve
_______ less salt would dissolve

 

2. Solubility of Liquids in Liquids

 

Solutes        Solubility in Water       Solubility in Toluene

 

Alcohol

Gasoline

Kerosene

Oil

 

What's the solubility of each solutes in water and toluene? How do you get the answer Wyzanters? Can you help me? :(

Answer 1

1. salt dissociates to a greater extent at higher temperature, which means the soluability constant of salt are increased at higher temperatures. 

 

2.Like  dissolves like. Alcohol with short carbon chains are considered polar because of greater polar characteristic, and alcolhol with really long carbon chains are considered non polar due to the fact the long carbon chain's non-polar characteristic. So small alcohols are soluable in water while big ones are not. 

 

Gasoline and kerosene are alkanes, which are just saturated hydrocarbons and non-polar, are not soluble in water but soluble in toluene. Oils are long hydrocarbon chains with a carboxylic group at one end. This long carbon chain makes it largely nonpolar, so insoluble in water but soluble in toluene

Answer 2

Hello Paige,

 

For the second question, you have to remember that "like dissolves like". So polar solutes will be dissolved by polar solvents and non-polar solutes will be dissolved by non-polar solvents.

 

This takes practice, but you have to pay attention to:

 

1) The shape of the molecule.

 

2) the Electronegativity of the atoms in the molecule.

 

Let's take water for example.

 

1)It is a "bent" shaped molecule with one Oxygen and two Hydrogen. This bent shape allows a "net dipole moment".

 

2) the electronegativity of the Oxygen atom is stronger than the electronegativity of the two Hydrogen atoms. This means that the electrons that are shared between oxygen and both hydrogen atoms are pulled closer to the oxygen. This gives the oxygen a partial negative charge and the Hydrogens a partial positive charge.

 

Since one end of the water molecule is negative (Oxygen) and the other end is positive (the Hydrogens), we say that the molecule is "polar". Think of the North and South pole. This is the same except we call one pole positive, and the other pole negative due to the difference in electronegativity.

 

So the question gives you two solvents: Water and Toluene. Water is polar, and Toluene is non-polar (because there is not a large difference in elecronegativity between the atoms in Toluene). Since like dissolves like, water will only dissolve a polar solute, alcohol is tho only polar solute of the answer choices. The other solutes are non-polar hydrocarbons, so toluene will dissolve them.

 

I know this was a lot, and the key to answering these types of questions is to be able to understand polarity, and  distinguish between polar and non-polar solvents and solutes. In order to do that, you have to pay attention to the molecular shape, and electronegativity.

 

Here are some wikipedia links that may clear things up:

https://en.wikipedia.org/wiki/Properties_of_water#Polarity_and_hydrogen_bonding

 

Read "Polarity and Hydrogen bonding", and "water as a solvent". They also have a nice image of the molecular shape.

 

Here is the link for Toluene: Notice there is no oxygen atom in the structure, only Carbons and Hydrogens. Since there is no big difference in electronegativity, the molecule is non-polar.

 

https://en.wikipedia.org/wiki/Toluene

 

Here are some more links explaining Electronegativity, and Polarity:

 

https://en.wikipedia.org/wiki/Electronegativity

 

https://en.wikipedia.org/wiki/Chemical_polarity

 

I hope this helps. Good luck, and do lots of problems!

Answer 3

The general rule is: solutes are more soluble in solvents at higher temperatures. That should guide you to the answer!