[填空题]
The table below shows the t)i33g(j/xl g/tl a ktdata gathered byd a /x*6fr8*sun cpd*d a chemist regarding substances A, B, *d/xarc snd u*df8*p6 and C. Using the data given, discuss which is a pure substance or a mixture. If the substance is a pure substance, determine whether it is an element or a compound.
Substance
Appearance
Melting point
Observed property
A
White crystalline solid
801$^{\circ}$
In aqueous solution, it reacts with silver nitrate forming a precipitate of silver chloride
B
Silver metallic appearance
660$^{\circ}$
Reacts with oxygen forming an oxide
C
Fine white crystalline solid
186$^{\circ}$-800$^{\circ}$
Readily dissolves in water
Substance A-
Substance B-
Substance C-
参考答案: 空格1: pure substance
空格2: compound
空格3: pure substance
空格4: element
空格5: mixture
本题详细解析:
Substance A has a distinct melting point, which means it has a definite composition, hence it is a pure substance. The precipitate formed is a product of a double displacement reaction, which means substance A is a compound.
Substance B also has a distinct melting point and is considered a pure substance. Substance B reacts with oxygen to form an oxide. This is an example of a synthesis reaction between an element (metal) and oxygen.
Substance C has no distinct melting point. This implies that two or more substances are combined physically as a mixture. Mixtures do not have a definite composition and distinct properties.
