If formula of sodium salt of an anion X is \(Na_2X\) , then the formula of its aluminium salt would be
Understanding Ionic Formulas and Salt Formation
The question asks us to determine the formula of the aluminium salt of an anion X, given that the formula of the sodium salt of the same anion X is \(Na_2X\).
To solve this, we first need to figure out the charge of the anion X based on the formula of the sodium salt. Then, we can combine this anion with the aluminium cation to find the formula of the aluminium salt.
Determining the Charge of Anion X
In the compound \(Na_2X\):
- Sodium (Na) is an alkali metal belonging to Group 1 of the periodic table. Elements in Group 1 typically form ions with a +1 charge (\(Na^+\)).
- The formula \(Na_2X\) indicates there are two sodium ions combined with one anion X.
- For the compound to be electrically neutral, the total positive charge must balance the total negative charge.
Let the charge of anion X be \(z\). The total positive charge from two sodium ions is \(2 \times (+1) = +2\). The total negative charge from one anion X is \(1 \times z = z\).
For a neutral compound:
\(\text{Total positive charge} + \text{Total negative charge} = 0\)
\(+2 + z = 0\)
\(z = -2\)
Therefore, the charge of the anion X is -2. We can represent the anion as \(X^{2-}\).
Determining the Formula of the Aluminium Salt
Now we need to form a salt using the aluminium cation and the anion \(X^{2-}\):
- Aluminium (Al) is a metal belonging to Group 13 of the periodic table. Aluminium typically forms ions with a +3 charge (\(Al^{3+}\)).
- The anion is \(X^{2-}\), which has a -2 charge.
To find the formula of the compound formed between \(Al^{3+}\) and \(X^{2-}\), we need to find the ratio of ions that results in a neutral compound. We can use the criss-cross method or find the least common multiple (LCM) of the charges' magnitudes (3 and 2).
The LCM of 3 and 2 is 6. We need a total positive charge of +6 and a total negative charge of -6.
- To get a total positive charge of +6 from \(Al^{3+}\) ions, we need \(6 / 3 = 2\) aluminium ions (\(2 \times +3 = +6\)).
- To get a total negative charge of -6 from \(X^{2-}\) ions, we need \(6 / 2 = 3\) X anions (\(3 \times -2 = -6\)).
So, the formula requires 2 aluminium ions (\(Al^{3+}\)) and 3 X anions (\(X^{2-}\)). The formula of the aluminium salt is \(Al_2X_3\).
Alternatively, using the criss-cross method:
Take the magnitude of the charge of \(Al^{3+}\) (which is 3) and make it the subscript for X.
Take the magnitude of the charge of \(X^{2-}\) (which is 2) and make it the subscript for Al.
\(Al^{\overset{3}{+}}X^{\overset{2}{-}} \rightarrow Al_2X_3\)
The resulting formula is \(Al_2X_3\).
| Salt Type | Cation | Anion Charge | Formula |
|---|---|---|---|
| Sodium Salt | \(Na^+\) (+1) | X (Determined) | \(Na_2X\) |
| Anion X | - | \(X^{2-}\) (-2) | - |
| Aluminium Salt | \(Al^{3+}\) (+3) | \(X^{2-}\) (-2) | \(Al_2X_3\) |
Thus, based on the formula of the sodium salt \(Na_2X\), we deduce the anion X has a charge of -2. Combining this \(X^{2-}\) anion with the typical aluminium cation \(Al^{3+}\) gives the formula \(Al_2X_3\) for the aluminium salt.
Revision Table: Common Ion Charges
| Element/Group | Typical Ion | Charge |
|---|---|---|
| Group 1 (Alkali Metals: Li, Na, K) | \(M^+\) | +1 |
| Group 2 (Alkaline Earth Metals: Mg, Ca, Ba) | \(M^{2+}\) | +2 |
| Group 13 (e.g., Al) | \(Al^{3+}\) | +3 |
| Group 17 (Halogens: F, Cl, Br, I) | \(X^{-}\) | -1 |
| Group 16 (e.g., O, S) | \(Y^{2-}\) | -2 |
| Group 15 (e.g., N, P) | \(Z^{3-}\) | -3 |
Understanding these common charges helps predict the formulas of many ionic compounds, including salts.
Additional Information: Ionic Compound Formulas
Ionic compounds are formed between metals and nonmetals. Metals lose electrons to form positively charged cations, while nonmetals gain electrons to form negatively charged anions. The formula of an ionic compound represents the simplest whole-number ratio of cations to anions needed to achieve electrical neutrality.
When writing the formula of an ionic compound:
- Write the symbol of the cation first, followed by the symbol of the anion.
- Determine the charge of each ion.
- Use subscripts to indicate the number of each ion needed to balance the charges, resulting in a net charge of zero. The magnitudes of the charges are used as subscripts (criss-cross method), and the subscripts are simplified to the lowest whole-number ratio.
- Polyatomic ions (ions made of multiple atoms) are treated as a single unit, and their formula is enclosed in parentheses if a subscript is required. In this problem, X is treated as a simple anion, though it could represent a polyatomic ion with a -2 charge.
This process ensures the compound is electrically neutral, which is a fundamental principle for ionic substances.
Important Questions from Basic Concepts of Chemistry
Which of the following pair is correct?
I. Isotopes – different mass numbers
II. Isobars – different atomic numbers
Which of the following is a zone of a flame?
I. Dark
II. Luminous
III. Non-Luminous
Sphalerite is an ore of:
Which of the following set contains same number of molecules?
A. 1 gram O 2, 2 grams SO 2
B. 1 gram CO 2, 1 gram N 2O
C. 1 gram O 2, 1 gram O 3
Which of the following cannot be cut by a knife ?
