Doubts regarding basic chemistry concepts

In summary, the law of reciprocal proportions states that the ratio of the masses in which two elements combine with a fixed mass of a third element will be a whole number multiple of the ratio in which those two elements combine with each other. This holds true as long as the order of the elements is maintained. However, if the order is reversed, the resulting ratio may not be a whole number multiple. This principle applies to both mass-to-mass and mole-to-mole ratios.
  • #1
donaldparida
146
10
Doubts regarding the law of reciprocal proportions: What i have understood by reading the definition is that the ratio of the masses in which two elements A and B combine with a fixed mass of a third element C, will be a whole number multiple of the ratio of the masses in which A and B combine with each other.
My question is that is order important here? Let A and C combine in the ratio a:c1 and let B and C combine in the ratio b:c2=((b*c1)/c2):c1.(by mass). Then according to the law of reciprocal proportions, a:((b*c1)/c2)=k (a:b) where k ia whole number. If we reverse the order in which we consider the mass of the elements in the ratio, will we get the same result then also? (Is ((b*c1)/c2):a=j (b:a) where j is a whole number in that case also).

Doubts regarding equivalent weight:I do understand the definition of equivalent weight but cannot make sense of it and understand the significance of the definition. What is the meaning of "parts by mass"
in it's definition and what is the use of equivalent weight?
 
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  • #2
Your concept is good but your numerical description using symbols is confusing. Maybe try again.

Combining ratios of elements really does make use of ratio IN MOLES. We use then a ratio of MASS to MOLES to make a conversion into PARTS BY MASS, if we want it; but finding the result as simple ratio between whole numbers takes more work/effort.
 
  • #3
Here is the numerical part with proper editing.
Let A and C combine in the ratio [itex]\frac{a}{c1}[/itex] and let B and C combine in the ratio [itex]\frac{b}{c2}=\frac{b*c1}{c1*c2}[/itex].(by mass). Then according to the law of reciprocal proportions, [itex]\frac{a*c2}{b*c1}[/itex]=k [itex]\frac{a}{b}[/itex] where k is whole number. If we reverse the order in which we consider the mass of the elements in the ratio, will we get the same result then also? (Is [itex]\frac{b*c1}{a*c2}[/itex]=j [itex]\frac{b}{a}[/itex] where j is a whole number in that case also). I had done some calculations and i found out that this is not true. So is this violating the law of reciprocal proportions?
 
  • #4
Many people learned compounds being made according to mole ratios, and reactions occurring along mole ratios of the reactants. Then people were taught about "molecular" weights and using them to convert moles to masses, and then people might have also been taught about gravimetric factors. Remember the word, "stoichiometry"?

If given reactants or products in grams or kilograms, they can be converted to moles, using their formula weights or molecular weights. If given reactants or products in moles, they can be converted to their masses using their formula weights or molecular weights.
 
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  • #5
If a*c2/b*c1 = k*a/b, it follows that the reciprocal b*c1/a*c2 = (1/k)*b/a. If k is a whole number, 1/k is not, unless k =1. So yes, order matters. A better statement of the principle would be that the ratio will be a whole number or reciprocal whole number (or perhaps, even more generally, the ratio of two whole numbers) multiple of the ratio in which A and B combine.
 

1. What is the difference between an atom and a molecule?

An atom is the smallest unit of matter that retains the properties of an element. It is composed of a nucleus containing protons and neutrons, and surrounded by electrons. A molecule, on the other hand, is made up of two or more atoms bonded together. In simpler terms, atoms are the building blocks of molecules.

2. What is the periodic table and why is it important in chemistry?

The periodic table is a tabular arrangement of all known elements, organized by their atomic number, electron configuration, and chemical properties. It is considered one of the most important tools in chemistry as it allows scientists to predict the behavior and properties of elements based on their position on the table.

3. What is the difference between an element and a compound?

An element is a pure substance made up of only one type of atom. It cannot be broken down into simpler substances through chemical reactions. A compound, on the other hand, is a substance made up of two or more different elements bonded together in a fixed ratio. Compounds can be broken down into smaller units through chemical reactions.

4. What is the difference between an ionic bond and a covalent bond?

An ionic bond is a type of chemical bond formed between two atoms with opposite charges. One atom gives up an electron to the other, resulting in a positively charged ion and a negatively charged ion that are then attracted to each other. A covalent bond, on the other hand, is formed when two atoms share electrons to achieve a more stable electron configuration. This results in a molecule being formed.

5. How do I determine the number of protons, neutrons, and electrons in an atom?

The number of protons in an atom is equal to its atomic number, which can be found on the periodic table. The number of neutrons can be calculated by subtracting the atomic number from the mass number of the element. The number of electrons is also equal to the atomic number, unless the atom is an ion, in which case the number of electrons will be either more or less than the atomic number depending on the charge of the ion.

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