<span>A theory that has been proven true repeatedly over time and never disproven is called a law</span>
Scientific modelling. In science, a model is a representation of an idea, an object or even a process or a system that is used to describe and explain phenomena that cannot be experienced directly. Models are central to what scientists do, both in their research as well as when communicating their explanations.
Answer:
Explanation:
Physical Change:
The changes that occur only due to change in shape or form but their chemical or internal composition remain unchanged.
These changes were reversible.
They have same chemical property.
These changes can be observed with naked eye.
Example
:
Water converting to Ice
Water converting to gas
In this water molecule remain the same only they rearrange themselves that change its state of mater not composition
Chemical changes:
The changes, that occur due to change in the composition of a substance and result in a different compound is known as chemical change.
These changes are irreversible
These changes occur due to chemical reactions
These may not be observed with naked eye
Example:
Combustion of fuel or wood: that oil or wood convert into energy, CO₂ and ash in case of wood
Boiling of egg: that change the chemical composition of protein in the egg
The reaction of Hydrogen and oxygen:
H₂ (g) + O₂ (g) -------------------------------------> 2H₂O (l)
Answer: Option D) 0.902M
Explanation:
Sodium chloride has a chemical formula of NaCl
Given that,
Amount of moles of NaCl (n) = ?
Mass of NaCl in grams = 145g
For molar mass of NaCl, use the molar masses:
Sodium, Na = 23g;
Chlorine,Cl = 35.5g
NaOH = (23g + 35.5g)
= 58.5g/mol
Since, amount of moles = mass in grams / molar mass
n = 145g / 58.5g/mol
n = 2.48 mole
Amount of moles of NaCl (n) = 2.48 mole
Volume of NaCl solution (v) = 2.75L
Concentration of NaCl solution (c) = ?
Since concentration (c) is obtained by dividing the amount of solute dissolved by the volume of solvent, hence
c = n / v
c = 2.48 mole / 2.75L
c = 0.9018M
Approximately, c = 0.902M
[c is the concentration in moles per litres which is also known as molarity]
Thus, the molarity of the solution is 0.902M